diff --git a/src/importsToResolve.js b/src/importsToResolve.js
index 01e20edf..631e260e 100644
--- a/src/importsToResolve.js
+++ b/src/importsToResolve.js
@@ -19,34 +19,56 @@ function importsToResolve(url) {
   // @see https://github.com/webpack-contrib/sass-loader/issues/167
   const ext = path.extname(request);
 
+  // In case there is module request, send this to webpack resolver
   if (matchModuleImport.test(url)) {
     return [request, url];
   }
 
-  // libsass' import algorithm works like this:
-
-  // In case there is a file extension...
-  //   - If the file is a CSS-file, do not include it all, but just link it via @import url().
-  //   - The exact file name must match (no auto-resolving of '_'-modules).
+  // Because @import is also defined in CSS, Sass needs a way of compiling plain CSS @imports without trying to import the files at compile time.
+  // To accomplish this, and to ensure SCSS is as much of a superset of CSS as possible, Sass will compile any @imports with the following characteristics to plain CSS imports:
+  //  - imports where the URL ends with .css.
+  //  - imports where the URL begins http:// or https://.
+  //  - imports where the URL is written as a url().
+  //  - imports that have media queries.
+  //
+  // The `node-sass` package sends `@import` ending on `.css` to importer, it is bug, so we skip resolve
   if (ext === '.css') {
     return [];
   }
 
+  const dirname = path.dirname(request);
+  const basename = path.basename(request);
+
+  // In case there is file extension:
+  //
+  // 1. Try to resolve `_` file.
+  // 2. Try to resolve file without `_`.
+  // 3. Send a original url to webpack resolver, maybe it is alias.
   if (['.scss', '.sass'].includes(ext)) {
-    return [request, url];
+    return [`${dirname}/_${basename}`, `${dirname}/${basename}`, url];
   }
 
-  // In case there is no file extension...
-  //   - Prefer modules starting with '_'.
-  //   - File extension precedence: .scss, .sass, .css.
-  const basename = path.basename(request);
-
+  // In case there is no file extension and filename starts with `_`:
+  //
+  // 1. Try to resolve files with `scss`, `sass` and `css` extensions.
+  // 2. Try to resolve directory with `_index` or `index` filename.
+  // 3. Send a original url to webpack resolver, maybe it is alias.
   if (basename.charAt(0) === '_') {
-    return [`${request}.scss`, `${request}.sass`, `${request}.css`, url];
+    return [
+      `${request}.scss`,
+      `${request}.sass`,
+      `${request}.css`,
+      request,
+      url,
+    ];
   }
 
-  const dirname = path.dirname(request);
-
+  // In case there is no file extension and filename doesn't start with `_`:
+  //
+  // 1. Try to resolve file starts with `_` and with extensions
+  // 2. Try to resolve file with extensions
+  // 3. Try to resolve directory with `_index` or `index` filename.
+  // 4. Send a original url to webpack resolver, maybe it is alias.
   return [
     `${dirname}/_${basename}.scss`,
     `${dirname}/_${basename}.sass`,
@@ -54,6 +76,7 @@ function importsToResolve(url) {
     `${request}.scss`,
     `${request}.sass`,
     `${request}.css`,
+    request,
     url,
   ];
 }
diff --git a/src/index.js b/src/index.js
index 9002136a..9cd37180 100644
--- a/src/index.js
+++ b/src/index.js
@@ -55,7 +55,8 @@ function loader(content) {
   // Supported since v4.36.0
   if (hasGetResolve(self)) {
     resolve = this.getResolve({
-      mainFields: ['sass', 'style', '...'],
+      mainFields: ['sass', 'style', 'main', '...'],
+      mainFiles: ['_index', 'index', '...'],
       extensions: ['.scss', '.sass', '.css', '...'],
     });
   }
diff --git a/test/__snapshots__/loader.test.js.snap b/test/__snapshots__/loader.test.js.snap
index 96cc0afd..8857356f 100644
--- a/test/__snapshots__/loader.test.js.snap
+++ b/test/__snapshots__/loader.test.js.snap
@@ -282,6 +282,22 @@ exports[`loader should work and ignore all css "@import" at-rules (node-sass) (s
 
 exports[`loader should work and ignore all css "@import" at-rules (node-sass) (scss): warnings 1`] = `Array []`;
 
+exports[`loader should work and use the "_index" file in package (dart-sass) (sass): errors 1`] = `Array []`;
+
+exports[`loader should work and use the "_index" file in package (dart-sass) (sass): warnings 1`] = `Array []`;
+
+exports[`loader should work and use the "_index" file in package (dart-sass) (scss): errors 1`] = `Array []`;
+
+exports[`loader should work and use the "_index" file in package (dart-sass) (scss): warnings 1`] = `Array []`;
+
+exports[`loader should work and use the "_index" file in package (node-sass) (sass): errors 1`] = `Array []`;
+
+exports[`loader should work and use the "_index" file in package (node-sass) (sass): warnings 1`] = `Array []`;
+
+exports[`loader should work and use the "_index" file in package (node-sass) (scss): errors 1`] = `Array []`;
+
+exports[`loader should work and use the "_index" file in package (node-sass) (scss): warnings 1`] = `Array []`;
+
 exports[`loader should work and use the "custom-sass" field (dart-sass) (sass): errors 1`] = `Array []`;
 
 exports[`loader should work and use the "custom-sass" field (dart-sass) (sass): warnings 1`] = `Array []`;
@@ -298,21 +314,53 @@ exports[`loader should work and use the "custom-sass" field (node-sass) (scss):
 
 exports[`loader should work and use the "custom-sass" field (node-sass) (scss): warnings 1`] = `Array []`;
 
-exports[`loader should work and use the "index" property in package (dart-sass) (sass): errors 1`] = `Array []`;
+exports[`loader should work and use the "index" file in package (dart-sass) (sass): errors 1`] = `Array []`;
+
+exports[`loader should work and use the "index" file in package (dart-sass) (sass): warnings 1`] = `Array []`;
+
+exports[`loader should work and use the "index" file in package (dart-sass) (scss): errors 1`] = `Array []`;
+
+exports[`loader should work and use the "index" file in package (dart-sass) (scss): warnings 1`] = `Array []`;
+
+exports[`loader should work and use the "index" file in package (node-sass) (sass): errors 1`] = `Array []`;
+
+exports[`loader should work and use the "index" file in package (node-sass) (sass): warnings 1`] = `Array []`;
+
+exports[`loader should work and use the "index" file in package (node-sass) (scss): errors 1`] = `Array []`;
+
+exports[`loader should work and use the "index" file in package (node-sass) (scss): warnings 1`] = `Array []`;
+
+exports[`loader should work and use the "index" file in package when the "index" value already in the "mainFiles" resolve option (dart-sass) (sass): errors 1`] = `Array []`;
 
-exports[`loader should work and use the "index" property in package (dart-sass) (sass): warnings 1`] = `Array []`;
+exports[`loader should work and use the "index" file in package when the "index" value already in the "mainFiles" resolve option (dart-sass) (sass): warnings 1`] = `Array []`;
 
-exports[`loader should work and use the "index" property in package (dart-sass) (scss): errors 1`] = `Array []`;
+exports[`loader should work and use the "index" file in package when the "index" value already in the "mainFiles" resolve option (dart-sass) (scss): errors 1`] = `Array []`;
 
-exports[`loader should work and use the "index" property in package (dart-sass) (scss): warnings 1`] = `Array []`;
+exports[`loader should work and use the "index" file in package when the "index" value already in the "mainFiles" resolve option (dart-sass) (scss): warnings 1`] = `Array []`;
 
-exports[`loader should work and use the "index" property in package (node-sass) (sass): errors 1`] = `Array []`;
+exports[`loader should work and use the "index" file in package when the "index" value already in the "mainFiles" resolve option (node-sass) (sass): errors 1`] = `Array []`;
 
-exports[`loader should work and use the "index" property in package (node-sass) (sass): warnings 1`] = `Array []`;
+exports[`loader should work and use the "index" file in package when the "index" value already in the "mainFiles" resolve option (node-sass) (sass): warnings 1`] = `Array []`;
 
-exports[`loader should work and use the "index" property in package (node-sass) (scss): errors 1`] = `Array []`;
+exports[`loader should work and use the "index" file in package when the "index" value already in the "mainFiles" resolve option (node-sass) (scss): errors 1`] = `Array []`;
 
-exports[`loader should work and use the "index" property in package (node-sass) (scss): warnings 1`] = `Array []`;
+exports[`loader should work and use the "index" file in package when the "index" value already in the "mainFiles" resolve option (node-sass) (scss): warnings 1`] = `Array []`;
+
+exports[`loader should work and use the "index" file in package when the "index" value is not in the "mainFiles" resolve option (dart-sass) (sass): errors 1`] = `Array []`;
+
+exports[`loader should work and use the "index" file in package when the "index" value is not in the "mainFiles" resolve option (dart-sass) (sass): warnings 1`] = `Array []`;
+
+exports[`loader should work and use the "index" file in package when the "index" value is not in the "mainFiles" resolve option (dart-sass) (scss): errors 1`] = `Array []`;
+
+exports[`loader should work and use the "index" file in package when the "index" value is not in the "mainFiles" resolve option (dart-sass) (scss): warnings 1`] = `Array []`;
+
+exports[`loader should work and use the "index" file in package when the "index" value is not in the "mainFiles" resolve option (node-sass) (sass): errors 1`] = `Array []`;
+
+exports[`loader should work and use the "index" file in package when the "index" value is not in the "mainFiles" resolve option (node-sass) (sass): warnings 1`] = `Array []`;
+
+exports[`loader should work and use the "index" file in package when the "index" value is not in the "mainFiles" resolve option (node-sass) (scss): errors 1`] = `Array []`;
+
+exports[`loader should work and use the "index" file in package when the "index" value is not in the "mainFiles" resolve option (node-sass) (scss): warnings 1`] = `Array []`;
 
 exports[`loader should work and use the "main" field (dart-sass) (sass): errors 1`] = `Array []`;
 
@@ -330,6 +378,38 @@ exports[`loader should work and use the "main" field (node-sass) (scss): errors
 
 exports[`loader should work and use the "main" field (node-sass) (scss): warnings 1`] = `Array []`;
 
+exports[`loader should work and use the "main" field when the "main" value already in the "mainFields" resolve option (dart-sass) (sass): errors 1`] = `Array []`;
+
+exports[`loader should work and use the "main" field when the "main" value already in the "mainFields" resolve option (dart-sass) (sass): warnings 1`] = `Array []`;
+
+exports[`loader should work and use the "main" field when the "main" value already in the "mainFields" resolve option (dart-sass) (scss): errors 1`] = `Array []`;
+
+exports[`loader should work and use the "main" field when the "main" value already in the "mainFields" resolve option (dart-sass) (scss): warnings 1`] = `Array []`;
+
+exports[`loader should work and use the "main" field when the "main" value already in the "mainFields" resolve option (node-sass) (sass): errors 1`] = `Array []`;
+
+exports[`loader should work and use the "main" field when the "main" value already in the "mainFields" resolve option (node-sass) (sass): warnings 1`] = `Array []`;
+
+exports[`loader should work and use the "main" field when the "main" value already in the "mainFields" resolve option (node-sass) (scss): errors 1`] = `Array []`;
+
+exports[`loader should work and use the "main" field when the "main" value already in the "mainFields" resolve option (node-sass) (scss): warnings 1`] = `Array []`;
+
+exports[`loader should work and use the "main" field when the "main" value is not in the "mainFields" resolve option (dart-sass) (sass): errors 1`] = `Array []`;
+
+exports[`loader should work and use the "main" field when the "main" value is not in the "mainFields" resolve option (dart-sass) (sass): warnings 1`] = `Array []`;
+
+exports[`loader should work and use the "main" field when the "main" value is not in the "mainFields" resolve option (dart-sass) (scss): errors 1`] = `Array []`;
+
+exports[`loader should work and use the "main" field when the "main" value is not in the "mainFields" resolve option (dart-sass) (scss): warnings 1`] = `Array []`;
+
+exports[`loader should work and use the "main" field when the "main" value is not in the "mainFields" resolve option (node-sass) (sass): errors 1`] = `Array []`;
+
+exports[`loader should work and use the "main" field when the "main" value is not in the "mainFields" resolve option (node-sass) (sass): warnings 1`] = `Array []`;
+
+exports[`loader should work and use the "main" field when the "main" value is not in the "mainFields" resolve option (node-sass) (scss): errors 1`] = `Array []`;
+
+exports[`loader should work and use the "main" field when the "main" value is not in the "mainFields" resolve option (node-sass) (scss): warnings 1`] = `Array []`;
+
 exports[`loader should work and use the "sass" field (dart-sass) (sass): errors 1`] = `Array []`;
 
 exports[`loader should work and use the "sass" field (dart-sass) (sass): warnings 1`] = `Array []`;
@@ -362,6 +442,54 @@ exports[`loader should work and use the "style" field (node-sass) (scss): errors
 
 exports[`loader should work and use the "style" field (node-sass) (scss): warnings 1`] = `Array []`;
 
+exports[`loader should work when "@import" at-rules starting with "_" (dart-sass) (sass): errors 1`] = `Array []`;
+
+exports[`loader should work when "@import" at-rules starting with "_" (dart-sass) (sass): warnings 1`] = `Array []`;
+
+exports[`loader should work when "@import" at-rules starting with "_" (dart-sass) (scss): errors 1`] = `Array []`;
+
+exports[`loader should work when "@import" at-rules starting with "_" (dart-sass) (scss): warnings 1`] = `Array []`;
+
+exports[`loader should work when "@import" at-rules starting with "_" (node-sass) (sass): errors 1`] = `Array []`;
+
+exports[`loader should work when "@import" at-rules starting with "_" (node-sass) (sass): warnings 1`] = `Array []`;
+
+exports[`loader should work when "@import" at-rules starting with "_" (node-sass) (scss): errors 1`] = `Array []`;
+
+exports[`loader should work when "@import" at-rules starting with "_" (node-sass) (scss): warnings 1`] = `Array []`;
+
+exports[`loader should work when "@import" at-rules with extensions (dart-sass) (sass): errors 1`] = `Array []`;
+
+exports[`loader should work when "@import" at-rules with extensions (dart-sass) (sass): warnings 1`] = `Array []`;
+
+exports[`loader should work when "@import" at-rules with extensions (dart-sass) (scss): errors 1`] = `Array []`;
+
+exports[`loader should work when "@import" at-rules with extensions (dart-sass) (scss): warnings 1`] = `Array []`;
+
+exports[`loader should work when "@import" at-rules with extensions (node-sass) (sass): errors 1`] = `Array []`;
+
+exports[`loader should work when "@import" at-rules with extensions (node-sass) (sass): warnings 1`] = `Array []`;
+
+exports[`loader should work when "@import" at-rules with extensions (node-sass) (scss): errors 1`] = `Array []`;
+
+exports[`loader should work when "@import" at-rules with extensions (node-sass) (scss): warnings 1`] = `Array []`;
+
+exports[`loader should work when "@import" at-rules without extensions and do not start with "_" (dart-sass) (sass): errors 1`] = `Array []`;
+
+exports[`loader should work when "@import" at-rules without extensions and do not start with "_" (dart-sass) (sass): warnings 1`] = `Array []`;
+
+exports[`loader should work when "@import" at-rules without extensions and do not start with "_" (dart-sass) (scss): errors 1`] = `Array []`;
+
+exports[`loader should work when "@import" at-rules without extensions and do not start with "_" (dart-sass) (scss): warnings 1`] = `Array []`;
+
+exports[`loader should work when "@import" at-rules without extensions and do not start with "_" (node-sass) (sass): errors 1`] = `Array []`;
+
+exports[`loader should work when "@import" at-rules without extensions and do not start with "_" (node-sass) (sass): warnings 1`] = `Array []`;
+
+exports[`loader should work when "@import" at-rules without extensions and do not start with "_" (node-sass) (scss): errors 1`] = `Array []`;
+
+exports[`loader should work when "@import" at-rules without extensions and do not start with "_" (node-sass) (scss): warnings 1`] = `Array []`;
+
 exports[`loader should work when an "@import" at-rule from scoped npm packages (dart-sass) (sass): errors 1`] = `Array []`;
 
 exports[`loader should work when an "@import" at-rule from scoped npm packages (dart-sass) (sass): warnings 1`] = `Array []`;
diff --git a/test/helpers/getPureCode.js b/test/helpers/getPureCode.js
index b5a20516..ecf8dc13 100644
--- a/test/helpers/getPureCode.js
+++ b/test/helpers/getPureCode.js
@@ -12,8 +12,10 @@ function getPureCode(testId, options) {
 
   delete sassOptions.implementation;
 
+  const isSass = /\.sass$/i.test(testId);
+
   if (sassOptions.data) {
-    sassOptions.indentedSyntax = /\.sass$/i.test(testId);
+    sassOptions.indentedSyntax = isSass;
     sassOptions.data = `$prepended-data: hotpink${
       sassOptions.indentedSyntax ? '\n' : ';'
     }${os.EOL}${fs.readFileSync(
@@ -38,6 +40,126 @@ function getPureCode(testId, options) {
     testFolder,
     'node_modules/scss-package-with-index/index.scss'
   );
+  const pathToSassPackageWithUnderscoreIndexFile = path.resolve(
+    testFolder,
+    'node_modules/sass-package-with-underscore-index/_index.sass'
+  );
+  const pathToSCSSPackageWithUnderscoreIndexFile = path.resolve(
+    testFolder,
+    'node_modules/scss-package-with-underscore-index/_index.scss'
+  );
+  const pathToSCSSUnderscoreDir = path.resolve(
+    testFolder,
+    'scss/_underscore-dir/_index.scss'
+  );
+  const pathToSCSSUnderscoreDir1 = path.resolve(
+    testFolder,
+    'scss/_underscore-dir-1/index.scss'
+  );
+  const pathToSCSSUnderscoreDir2 = path.resolve(
+    testFolder,
+    'scss/_underscore-dir-2/_index.sass'
+  );
+  const pathToSCSSUnderscoreDir3 = path.resolve(
+    testFolder,
+    'scss/_underscore-dir-3/index.sass'
+  );
+  // Avoid `.css` extensions because `node-sass` doesn't compile them
+  const pathToSCSSUnderscoreDir4 = path.resolve(
+    testFolder,
+    'scss/_underscore-dir-4/_index'
+  );
+  // Avoid `.css` extensions because `node-sass` doesn't compile them
+  const pathToSCSSUnderscoreDir5 = path.resolve(
+    testFolder,
+    'scss/_underscore-dir-5/index'
+  );
+  const pathToSassUnderscoreDir = path.resolve(
+    testFolder,
+    'sass/_underscore-dir/_index.sass'
+  );
+  const pathToSassUnderscoreDir1 = path.resolve(
+    testFolder,
+    'sass/_underscore-dir-1/index.sass'
+  );
+  const pathToSassUnderscoreDir2 = path.resolve(
+    testFolder,
+    'sass/_underscore-dir-2/_index.scss'
+  );
+  const pathToSassUnderscoreDir3 = path.resolve(
+    testFolder,
+    'sass/_underscore-dir-3/index.scss'
+  );
+  // Avoid `.css` extensions because `node-sass` doesn't compile them
+  const pathToSassUnderscoreDir4 = path.resolve(
+    testFolder,
+    'sass/_underscore-dir-4/_index'
+  );
+  // Avoid `.css` extensions because `node-sass` doesn't compile them
+  const pathToSassUnderscoreDir5 = path.resolve(
+    testFolder,
+    'sass/_underscore-dir-5/index'
+  );
+  const pathToSCSSWord6 = path.resolve(testFolder, 'scss/word-6/_index.scss');
+  const pathToSCSSWord7 = path.resolve(testFolder, 'scss/word-7/index.scss');
+  const pathToSCSSWord8 = path.resolve(testFolder, 'scss/word-8/index.sass');
+  const pathToSCSSWord9 = path.resolve(testFolder, 'scss/word-9/index.sass');
+  const pathToSCSSWord10 = path.resolve(testFolder, 'scss/word-10/_index');
+  const pathToSCSSWord11 = path.resolve(testFolder, 'scss/word-11/index');
+  const pathToSCSSDirectory6 = path.resolve(
+    testFolder,
+    'scss/directory-6/file/_index.scss'
+  );
+  const pathToSCSSDirectory7 = path.resolve(
+    testFolder,
+    'scss/directory-7/file/index.scss'
+  );
+  const pathToSCSSDirectory8 = path.resolve(
+    testFolder,
+    'scss/directory-8/file/_index.sass'
+  );
+  const pathToSCSSDirectory9 = path.resolve(
+    testFolder,
+    'scss/directory-9/file/index.sass'
+  );
+  const pathToSCSSDirectory10 = path.resolve(
+    testFolder,
+    'scss/directory-10/file/index'
+  );
+  const pathToSCSSDirectory11 = path.resolve(
+    testFolder,
+    'scss/directory-11/file/index'
+  );
+  const pathToSassWord6 = path.resolve(testFolder, 'sass/word-6/_index.sass');
+  const pathToSassWord7 = path.resolve(testFolder, 'sass/word-7/index.sass');
+  const pathToSassWord8 = path.resolve(testFolder, 'sass/word-8/index.scss');
+  const pathToSassWord9 = path.resolve(testFolder, 'sass/word-9/index.scss');
+  const pathToSassWord10 = path.resolve(testFolder, 'sass/word-10/_index');
+  const pathToSassWord11 = path.resolve(testFolder, 'sass/word-11/index');
+  const pathToSassDirectory6 = path.resolve(
+    testFolder,
+    'sass/directory-6/file/_index.sass'
+  );
+  const pathToSassDirectory7 = path.resolve(
+    testFolder,
+    'sass/directory-7/file/index.sass'
+  );
+  const pathToSassDirectory8 = path.resolve(
+    testFolder,
+    'sass/directory-8/file/_index.scss'
+  );
+  const pathToSassDirectory9 = path.resolve(
+    testFolder,
+    'sass/directory-9/file/index.scss'
+  );
+  const pathToSassDirectory10 = path.resolve(
+    testFolder,
+    'sass/directory-10/file/index'
+  );
+  const pathToSassDirectory11 = path.resolve(
+    testFolder,
+    'sass/directory-11/file/index'
+  );
   const pathToAlias = path.resolve(
     testFolder,
     path.extname(testId).slice(1),
@@ -109,11 +231,386 @@ function getPureCode(testId, options) {
           };
         }
 
+        if (url === '~sass-package-with-underscore-index') {
+          return {
+            file: pathToSassPackageWithUnderscoreIndexFile,
+          };
+        }
+
         if (url === '~scss-package-with-index') {
           return {
             file: pathToSCSSPackageWithIndexFile,
           };
         }
+
+        if (url === '~scss-package-with-underscore-index') {
+          return {
+            file: pathToSCSSPackageWithUnderscoreIndexFile,
+          };
+        }
+
+        // Fallback for `node-sass` what is not supported `index` and `_index` resolutions
+        if (!isSass) {
+          if (
+            url === '_underscore-dir' ||
+            url === './_underscore-dir' ||
+            url === '../scss/_underscore-dir'
+          ) {
+            return {
+              file: pathToSCSSUnderscoreDir,
+            };
+          }
+
+          if (
+            url === '_underscore-dir-1' ||
+            url === './_underscore-dir-1' ||
+            url === '../scss/_underscore-dir-1'
+          ) {
+            return {
+              file: pathToSCSSUnderscoreDir1,
+            };
+          }
+
+          if (
+            url === '_underscore-dir-2' ||
+            url === './_underscore-dir-2' ||
+            url === '../scss/_underscore-dir-2'
+          ) {
+            return {
+              file: pathToSCSSUnderscoreDir2,
+            };
+          }
+
+          if (
+            url === '_underscore-dir-3' ||
+            url === './_underscore-dir-3' ||
+            url === '../scss/_underscore-dir-3'
+          ) {
+            return {
+              file: pathToSCSSUnderscoreDir3,
+            };
+          }
+
+          if (
+            url === '_underscore-dir-4' ||
+            url === './_underscore-dir-4' ||
+            url === '../scss/_underscore-dir-4'
+          ) {
+            return {
+              file: pathToSCSSUnderscoreDir4,
+            };
+          }
+
+          if (
+            url === '_underscore-dir-5' ||
+            url === './_underscore-dir-5' ||
+            url === '../scss/_underscore-dir-5'
+          ) {
+            return {
+              file: pathToSCSSUnderscoreDir5,
+            };
+          }
+
+          if (
+            url === 'word-6' ||
+            url === './word-6' ||
+            url === '../scss/word-6'
+          ) {
+            return {
+              file: pathToSCSSWord6,
+            };
+          }
+
+          if (
+            url === 'word-7' ||
+            url === './word-7' ||
+            url === '../scss/word-7'
+          ) {
+            return {
+              file: pathToSCSSWord7,
+            };
+          }
+
+          if (
+            url === 'word-8' ||
+            url === './word-8' ||
+            url === '../scss/word-8'
+          ) {
+            return {
+              file: pathToSCSSWord8,
+            };
+          }
+
+          if (
+            url === 'word-9' ||
+            url === './word-9' ||
+            url === '../scss/word-9'
+          ) {
+            return {
+              file: pathToSCSSWord9,
+            };
+          }
+
+          if (
+            url === 'word-10' ||
+            url === './word-10' ||
+            url === '../scss/word-10'
+          ) {
+            return {
+              file: pathToSCSSWord10,
+            };
+          }
+
+          if (
+            url === 'word-11' ||
+            url === './word-11' ||
+            url === '../scss/word-11'
+          ) {
+            return {
+              file: pathToSCSSWord11,
+            };
+          }
+
+          if (
+            url === 'directory-6/file' ||
+            url === './directory-6/file' ||
+            url === '../scss/directory-6/file'
+          ) {
+            return {
+              file: pathToSCSSDirectory6,
+            };
+          }
+
+          if (
+            url === 'directory-7/file' ||
+            url === './directory-7/file' ||
+            url === '../scss/directory-7/file'
+          ) {
+            return {
+              file: pathToSCSSDirectory7,
+            };
+          }
+
+          if (
+            url === 'directory-8/file' ||
+            url === './directory-8/file' ||
+            url === '../scss/directory-8/file'
+          ) {
+            return {
+              file: pathToSCSSDirectory8,
+            };
+          }
+
+          if (
+            url === 'directory-9/file' ||
+            url === './directory-9/file' ||
+            url === '../scss/directory-9/file'
+          ) {
+            return {
+              file: pathToSCSSDirectory9,
+            };
+          }
+
+          if (
+            url === 'directory-10/file' ||
+            url === './directory-10/file' ||
+            url === '../scss/directory-10/file'
+          ) {
+            return {
+              file: pathToSCSSDirectory10,
+            };
+          }
+
+          if (
+            url === 'directory-11/file' ||
+            url === './directory-11/file' ||
+            url === '../scss/directory-11/file'
+          ) {
+            return {
+              file: pathToSCSSDirectory11,
+            };
+          }
+        } else {
+          if (
+            url === '_underscore-dir' ||
+            url === './_underscore-dir' ||
+            url === '../sass/_underscore-dir'
+          ) {
+            return {
+              file: pathToSassUnderscoreDir,
+            };
+          }
+
+          if (
+            url === '_underscore-dir-1' ||
+            url === './_underscore-dir-1' ||
+            url === '../sass/_underscore-dir-1'
+          ) {
+            return {
+              file: pathToSassUnderscoreDir1,
+            };
+          }
+
+          if (
+            url === '_underscore-dir-2' ||
+            url === './_underscore-dir-2' ||
+            url === '../sass/_underscore-dir-2'
+          ) {
+            return {
+              file: pathToSassUnderscoreDir2,
+            };
+          }
+
+          if (
+            url === '_underscore-dir-3' ||
+            url === './_underscore-dir-3' ||
+            url === '../sass/_underscore-dir-3'
+          ) {
+            return {
+              file: pathToSassUnderscoreDir3,
+            };
+          }
+
+          if (
+            url === '_underscore-dir-4' ||
+            url === './_underscore-dir-4' ||
+            url === '../sass/_underscore-dir-4'
+          ) {
+            return {
+              file: pathToSassUnderscoreDir4,
+            };
+          }
+
+          if (
+            url === '_underscore-dir-5' ||
+            url === './_underscore-dir-5' ||
+            url === '../sass/_underscore-dir-5'
+          ) {
+            return {
+              file: pathToSassUnderscoreDir5,
+            };
+          }
+
+          if (
+            url === 'word-6' ||
+            url === './word-6' ||
+            url === '../sass/word-6'
+          ) {
+            return {
+              file: pathToSassWord6,
+            };
+          }
+
+          if (
+            url === 'word-7' ||
+            url === './word-7' ||
+            url === '../sass/word-7'
+          ) {
+            return {
+              file: pathToSassWord7,
+            };
+          }
+
+          if (
+            url === 'word-8' ||
+            url === './word-8' ||
+            url === '../sass/word-8'
+          ) {
+            return {
+              file: pathToSassWord8,
+            };
+          }
+
+          if (
+            url === 'word-9' ||
+            url === './word-9' ||
+            url === '../sass/word-9'
+          ) {
+            return {
+              file: pathToSassWord9,
+            };
+          }
+
+          if (
+            url === 'word-10' ||
+            url === './word-10' ||
+            url === '../sass/word-10'
+          ) {
+            return {
+              file: pathToSassWord10,
+            };
+          }
+
+          if (
+            url === 'word-11' ||
+            url === './word-11' ||
+            url === '../sass/word-11'
+          ) {
+            return {
+              file: pathToSassWord11,
+            };
+          }
+
+          if (
+            url === 'directory-6/file' ||
+            url === './directory-6/file' ||
+            url === '../sass/directory-6/file'
+          ) {
+            return {
+              file: pathToSassDirectory6,
+            };
+          }
+
+          if (
+            url === 'directory-7/file' ||
+            url === './directory-7/file' ||
+            url === '../sass/directory-7/file'
+          ) {
+            return {
+              file: pathToSassDirectory7,
+            };
+          }
+
+          if (
+            url === 'directory-8/file' ||
+            url === './directory-8/file' ||
+            url === '../sass/directory-8/file'
+          ) {
+            return {
+              file: pathToSassDirectory8,
+            };
+          }
+
+          if (
+            url === 'directory-9/file' ||
+            url === './directory-9/file' ||
+            url === '../sass/directory-9/file'
+          ) {
+            return {
+              file: pathToSassDirectory9,
+            };
+          }
+
+          if (
+            url === 'directory-10/file' ||
+            url === './directory-10/file' ||
+            url === '../sass/directory-10/file'
+          ) {
+            return {
+              file: pathToSassDirectory10,
+            };
+          }
+
+          if (
+            url === 'directory-11/file' ||
+            url === './directory-11/file' ||
+            url === '../sass/directory-11/file'
+          ) {
+            return {
+              file: pathToSassDirectory11,
+            };
+          }
+        }
       }
 
       // eslint-disable-next-line no-param-reassign
diff --git a/test/loader.test.js b/test/loader.test.js
index 27101841..40c33585 100644
--- a/test/loader.test.js
+++ b/test/loader.test.js
@@ -265,6 +265,48 @@ describe('loader', () => {
         expect(stats.compilation.errors).toMatchSnapshot('errors');
       });
 
+      it(`should work when "@import" at-rules with extensions (${implementationName}) (${syntax})`, async () => {
+        const testId = getTestId('import-with-extension', syntax);
+        const options = {
+          implementation: getImplementationByName(implementationName),
+        };
+        const stats = await compile(testId, { loader: { options } });
+
+        expect(getCode(stats).content).toBe(getPureCode(testId, options));
+
+        expect(stats.compilation.warnings).toMatchSnapshot('warnings');
+        expect(stats.compilation.errors).toMatchSnapshot('errors');
+      });
+
+      it(`should work when "@import" at-rules starting with "_" (${implementationName}) (${syntax})`, async () => {
+        const testId = getTestId('import-with-underscore', syntax);
+        const options = {
+          implementation: getImplementationByName(implementationName),
+        };
+        const stats = await compile(testId, { loader: { options } });
+
+        expect(getCode(stats).content).toBe(getPureCode(testId, options));
+
+        expect(stats.compilation.warnings).toMatchSnapshot('warnings');
+        expect(stats.compilation.errors).toMatchSnapshot('errors');
+      });
+
+      it(`should work when "@import" at-rules without extensions and do not start with "_" (${implementationName}) (${syntax})`, async () => {
+        const testId = getTestId(
+          'import-without-extension-and-underscore',
+          syntax
+        );
+        const options = {
+          implementation: getImplementationByName(implementationName),
+        };
+        const stats = await compile(testId, { loader: { options } });
+
+        expect(getCode(stats).content).toBe(getPureCode(testId, options));
+
+        expect(stats.compilation.warnings).toMatchSnapshot('warnings');
+        expect(stats.compilation.errors).toMatchSnapshot('errors');
+      });
+
       it(`should work and use the "sass" field (${implementationName}) (${syntax})`, async () => {
         const testId = getTestId('import-sass-field', syntax);
         const options = {
@@ -304,6 +346,36 @@ describe('loader', () => {
         expect(stats.compilation.errors).toMatchSnapshot('errors');
       });
 
+      it(`should work and use the "main" field when the "main" value is not in the "mainFields" resolve option (${implementationName}) (${syntax})`, async () => {
+        const testId = getTestId('import-main-field', syntax);
+        const options = {
+          implementation: getImplementationByName(implementationName),
+        };
+        const stats = await compile(testId, {
+          loader: { options, resolve: { mainFields: [] } },
+        });
+
+        expect(getCode(stats).content).toBe(getPureCode(testId, options));
+
+        expect(stats.compilation.warnings).toMatchSnapshot('warnings');
+        expect(stats.compilation.errors).toMatchSnapshot('errors');
+      });
+
+      it(`should work and use the "main" field when the "main" value already in the "mainFields" resolve option (${implementationName}) (${syntax})`, async () => {
+        const testId = getTestId('import-main-field', syntax);
+        const options = {
+          implementation: getImplementationByName(implementationName),
+        };
+        const stats = await compile(testId, {
+          loader: { options, resolve: { mainFields: ['main', '...'] } },
+        });
+
+        expect(getCode(stats).content).toBe(getPureCode(testId, options));
+
+        expect(stats.compilation.warnings).toMatchSnapshot('warnings');
+        expect(stats.compilation.errors).toMatchSnapshot('errors');
+      });
+
       it(`should work and use the "custom-sass" field (${implementationName}) (${syntax})`, async () => {
         const testId = getTestId('import-custom-sass-field', syntax);
         const options = {
@@ -319,11 +391,54 @@ describe('loader', () => {
         expect(stats.compilation.errors).toMatchSnapshot('errors');
       });
 
-      it(`should work and use the "index" property in package (${implementationName}) (${syntax})`, async () => {
+      it(`should work and use the "index" file in package (${implementationName}) (${syntax})`, async () => {
+        const testId = getTestId('import-index', syntax);
+        const options = {
+          implementation: getImplementationByName(implementationName),
+        };
+        const stats = await compile(testId, { loader: { options } });
+
+        expect(getCode(stats).content).toBe(getPureCode(testId, options));
+
+        expect(stats.compilation.warnings).toMatchSnapshot('warnings');
+        expect(stats.compilation.errors).toMatchSnapshot('errors');
+      });
+
+      it(`should work and use the "index" file in package when the "index" value is not in the "mainFiles" resolve option (${implementationName}) (${syntax})`, async () => {
+        const testId = getTestId('import-index', syntax);
+        const options = {
+          implementation: getImplementationByName(implementationName),
+        };
+        const stats = await compile(testId, {
+          loader: { options, resolve: { mainFiles: [] } },
+        });
+
+        expect(getCode(stats).content).toBe(getPureCode(testId, options));
+
+        expect(stats.compilation.warnings).toMatchSnapshot('warnings');
+        expect(stats.compilation.errors).toMatchSnapshot('errors');
+      });
+
+      it(`should work and use the "index" file in package when the "index" value already in the "mainFiles" resolve option (${implementationName}) (${syntax})`, async () => {
         const testId = getTestId('import-index', syntax);
         const options = {
           implementation: getImplementationByName(implementationName),
         };
+        const stats = await compile(testId, {
+          loader: { options, resolve: { mainFiles: ['index', '...'] } },
+        });
+
+        expect(getCode(stats).content).toBe(getPureCode(testId, options));
+
+        expect(stats.compilation.warnings).toMatchSnapshot('warnings');
+        expect(stats.compilation.errors).toMatchSnapshot('errors');
+      });
+
+      it(`should work and use the "_index" file in package (${implementationName}) (${syntax})`, async () => {
+        const testId = getTestId('import-_index', syntax);
+        const options = {
+          implementation: getImplementationByName(implementationName),
+        };
         const stats = await compile(testId, { loader: { options } });
 
         expect(getCode(stats).content).toBe(getPureCode(testId, options));
diff --git a/test/node_modules/sass-package-with-underscore-index/_index.sass b/test/node_modules/sass-package-with-underscore-index/_index.sass
new file mode 100644
index 00000000..aabe2c18
--- /dev/null
+++ b/test/node_modules/sass-package-with-underscore-index/_index.sass
@@ -0,0 +1,2 @@
+a
+  color: red
diff --git a/test/node_modules/scss-package-with-underscore-index/_index.scss b/test/node_modules/scss-package-with-underscore-index/_index.scss
new file mode 100644
index 00000000..fdece7b4
--- /dev/null
+++ b/test/node_modules/scss-package-with-underscore-index/_index.scss
@@ -0,0 +1,3 @@
+a {
+  color: red;
+}
diff --git a/test/sass/_example-2.sass b/test/sass/_example-2.sass
new file mode 100644
index 00000000..50043c99
--- /dev/null
+++ b/test/sass/_example-2.sass
@@ -0,0 +1,2 @@
+.example-2
+  color: blue
diff --git a/test/sass/_example-3.SASS b/test/sass/_example-3.SASS
new file mode 100644
index 00000000..00d28267
--- /dev/null
+++ b/test/sass/_example-3.SASS
@@ -0,0 +1,2 @@
+.example-2
+  color: black
diff --git a/test/sass/_underscore-dir-1/index.sass b/test/sass/_underscore-dir-1/index.sass
new file mode 100644
index 00000000..add11dfa
--- /dev/null
+++ b/test/sass/_underscore-dir-1/index.sass
@@ -0,0 +1,2 @@
+.underscore-dir-1-index
+  color: goldenrod
diff --git a/test/sass/_underscore-dir-2/_index.scss b/test/sass/_underscore-dir-2/_index.scss
new file mode 100644
index 00000000..bca93144
--- /dev/null
+++ b/test/sass/_underscore-dir-2/_index.scss
@@ -0,0 +1,3 @@
+.underscore-dir-2-index {
+  color: mediumpurple;
+}
diff --git a/test/sass/_underscore-dir-3/index.scss b/test/sass/_underscore-dir-3/index.scss
new file mode 100644
index 00000000..52766094
--- /dev/null
+++ b/test/sass/_underscore-dir-3/index.scss
@@ -0,0 +1,4 @@
+.underscore-dir-3-index {
+  color: bisque;
+}
+
diff --git a/test/sass/_underscore-dir-4/_index.css b/test/sass/_underscore-dir-4/_index.css
new file mode 100644
index 00000000..fb53ce04
--- /dev/null
+++ b/test/sass/_underscore-dir-4/_index.css
@@ -0,0 +1,3 @@
+.underscore-dir-4-index {
+  color: maroon;
+}
diff --git a/test/sass/_underscore-dir-5/index.css b/test/sass/_underscore-dir-5/index.css
new file mode 100644
index 00000000..69c5ce54
--- /dev/null
+++ b/test/sass/_underscore-dir-5/index.css
@@ -0,0 +1,3 @@
+.underscore-dir-5-index {
+  color: magenta;
+}
diff --git a/test/sass/_underscore-dir/_index.sass b/test/sass/_underscore-dir/_index.sass
new file mode 100644
index 00000000..5141075b
--- /dev/null
+++ b/test/sass/_underscore-dir/_index.sass
@@ -0,0 +1,2 @@
+.underscore-dir-index
+  color: goldenrod
diff --git a/test/sass/_underscore-file-1.sass b/test/sass/_underscore-file-1.sass
new file mode 100644
index 00000000..6a9a21fb
--- /dev/null
+++ b/test/sass/_underscore-file-1.sass
@@ -0,0 +1,2 @@
+.underscore-1
+  color: cadetblue
diff --git a/test/sass/_underscore-file-2.scss b/test/sass/_underscore-file-2.scss
new file mode 100644
index 00000000..52c0ec81
--- /dev/null
+++ b/test/sass/_underscore-file-2.scss
@@ -0,0 +1,3 @@
+.underscore-2 {
+  color: azure;
+}
diff --git a/test/sass/_underscore-file-3.css b/test/sass/_underscore-file-3.css
new file mode 100644
index 00000000..c7c32e7e
--- /dev/null
+++ b/test/sass/_underscore-file-3.css
@@ -0,0 +1,3 @@
+.underscore-3 {
+  color: chocolate;
+}
diff --git a/test/sass/_underscore-file.sass b/test/sass/_underscore-file.sass
new file mode 100644
index 00000000..3a742217
--- /dev/null
+++ b/test/sass/_underscore-file.sass
@@ -0,0 +1,2 @@
+.underscore
+  color: greenyellow
diff --git a/test/sass/_word-1.scss b/test/sass/_word-1.scss
new file mode 100644
index 00000000..18b2148d
--- /dev/null
+++ b/test/sass/_word-1.scss
@@ -0,0 +1,3 @@
+.word-1 {
+  color: black;
+}
diff --git a/test/sass/_word-2.css b/test/sass/_word-2.css
new file mode 100644
index 00000000..8d9432e7
--- /dev/null
+++ b/test/sass/_word-2.css
@@ -0,0 +1,3 @@
+.word-2 {
+  color: aquamarine;
+}
diff --git a/test/sass/_word.sass b/test/sass/_word.sass
new file mode 100644
index 00000000..0f0934c4
--- /dev/null
+++ b/test/sass/_word.sass
@@ -0,0 +1,2 @@
+.word
+  color: red
diff --git a/test/sass/directory-1/file.sass b/test/sass/directory-1/file.sass
new file mode 100644
index 00000000..e648aef9
--- /dev/null
+++ b/test/sass/directory-1/file.sass
@@ -0,0 +1,2 @@
+.directory-1-file
+  color: #000066
diff --git a/test/sass/directory-10/file/_index.css b/test/sass/directory-10/file/_index.css
new file mode 100644
index 00000000..25209b13
--- /dev/null
+++ b/test/sass/directory-10/file/_index.css
@@ -0,0 +1,3 @@
+.directory-10-file {
+  color: #bbb;
+}
diff --git a/test/sass/directory-11/file/index.css b/test/sass/directory-11/file/index.css
new file mode 100644
index 00000000..39247396
--- /dev/null
+++ b/test/sass/directory-11/file/index.css
@@ -0,0 +1,3 @@
+.directory-10-file {
+  color: #ccb;
+}
diff --git a/test/sass/directory-2/_file.scss b/test/sass/directory-2/_file.scss
new file mode 100644
index 00000000..258ea2e3
--- /dev/null
+++ b/test/sass/directory-2/_file.scss
@@ -0,0 +1,3 @@
+.directory-2-file {
+  color: #7f7f7f;
+}
diff --git a/test/sass/directory-3/file.scss b/test/sass/directory-3/file.scss
new file mode 100644
index 00000000..bd376ee5
--- /dev/null
+++ b/test/sass/directory-3/file.scss
@@ -0,0 +1,3 @@
+.directory-3-file {
+  color: #7ff;
+}
diff --git a/test/sass/directory-4/_file.css b/test/sass/directory-4/_file.css
new file mode 100644
index 00000000..7de4a4db
--- /dev/null
+++ b/test/sass/directory-4/_file.css
@@ -0,0 +1,3 @@
+.directory-4-file {
+  color: #77ffff;
+}
diff --git a/test/sass/directory-5/file.css b/test/sass/directory-5/file.css
new file mode 100644
index 00000000..752d87b1
--- /dev/null
+++ b/test/sass/directory-5/file.css
@@ -0,0 +1,3 @@
+.directory-4-file {
+  color: #777;
+}
diff --git a/test/sass/directory-6/file/_index.sass b/test/sass/directory-6/file/_index.sass
new file mode 100644
index 00000000..94d9525a
--- /dev/null
+++ b/test/sass/directory-6/file/_index.sass
@@ -0,0 +1,2 @@
+.directory-6-file
+  color: #faf
diff --git a/test/sass/directory-7/file/index.sass b/test/sass/directory-7/file/index.sass
new file mode 100644
index 00000000..bcb6c078
--- /dev/null
+++ b/test/sass/directory-7/file/index.sass
@@ -0,0 +1,2 @@
+.directory-7-file
+  color: #afa
diff --git a/test/sass/directory-8/file/_index.scss b/test/sass/directory-8/file/_index.scss
new file mode 100644
index 00000000..d7418452
--- /dev/null
+++ b/test/sass/directory-8/file/_index.scss
@@ -0,0 +1,3 @@
+.directory-8-file {
+  color: #aaf;
+}
diff --git a/test/sass/directory-9/file/index.scss b/test/sass/directory-9/file/index.scss
new file mode 100644
index 00000000..7dacff31
--- /dev/null
+++ b/test/sass/directory-9/file/index.scss
@@ -0,0 +1,3 @@
+.directory-9-file {
+  color: #ffa;
+}
diff --git a/test/sass/directory/_file.sass b/test/sass/directory/_file.sass
new file mode 100644
index 00000000..8cf424d9
--- /dev/null
+++ b/test/sass/directory/_file.sass
@@ -0,0 +1,2 @@
+.directory-file
+  color: #000066
diff --git a/test/sass/example-1.SASS b/test/sass/example-1.SASS
new file mode 100644
index 00000000..c5309121
--- /dev/null
+++ b/test/sass/example-1.SASS
@@ -0,0 +1,2 @@
+.example-1
+  color: green
diff --git a/test/sass/example.sass b/test/sass/example.sass
new file mode 100644
index 00000000..9fc5d290
--- /dev/null
+++ b/test/sass/example.sass
@@ -0,0 +1,2 @@
+.example
+  color: red
diff --git a/test/sass/import-_index.sass b/test/sass/import-_index.sass
new file mode 100644
index 00000000..2f3a379a
--- /dev/null
+++ b/test/sass/import-_index.sass
@@ -0,0 +1 @@
+@import "~sass-package-with-underscore-index"
diff --git a/test/sass/import-with-extension.sass b/test/sass/import-with-extension.sass
new file mode 100644
index 00000000..f092e19c
--- /dev/null
+++ b/test/sass/import-with-extension.sass
@@ -0,0 +1,18 @@
+@import "example.sass"
+@import "./example.sass"
+@import "../sass/example.sass"
+// TODO https://github.com/sass/dart-sass/issues/798#issuecomment-521229911
+// @import "example-1.SASS"
+@import "example-2.sass"
+@import "./example-2.sass"
+@import "../sass/example-2.sass"
+// TODO https://github.com/sass/dart-sass/issues/798#issuecomment-521229911
+// @import "example-3.SASS"
+@import "nested/example-4.sass"
+@import "./nested/example-4.sass"
+@import "../sass/nested/example-4.sass"
+@import "nested/example-5.sass"
+@import "./nested/example-5.sass"
+@import "../sass/nested/example-5.sass"
+// TODO https://github.com/sass/dart-sass/issues/798#issuecomment-521229911
+// @import "nested/example-6.SASS";
diff --git a/test/sass/import-with-underscore.sass b/test/sass/import-with-underscore.sass
new file mode 100644
index 00000000..bf4dee8b
--- /dev/null
+++ b/test/sass/import-with-underscore.sass
@@ -0,0 +1,112 @@
+@import "_underscore-file"
+@import "underscore-file"
+@import "./_underscore-file"
+@import "./underscore-file"
+@import "../sass/_underscore-file"
+@import "../sass/underscore-file"
+@import "_underscore-file.sass"
+@import "./_underscore-file.sass"
+@import "../sass/_underscore-file.sass"
+@import "../sass/underscore-file.sass"
+// SASS
+@import "_underscore-file-1"
+@import "underscore-file-1"
+@import "./_underscore-file-1"
+@import "./underscore-file-1"
+@import "../sass/_underscore-file-1"
+@import "../sass/underscore-file-1"
+@import "_underscore-file-1.sass"
+@import "underscore-file-1.sass"
+@import "./_underscore-file-1.sass"
+@import "./underscore-file-1.sass"
+@import "../sass/_underscore-file-1.sass"
+@import "../sass/underscore-file-1.sass"
+// SCSS
+@import "_underscore-file-2"
+@import "underscore-file-2"
+@import "./_underscore-file-2"
+@import "./underscore-file-2"
+@import "../sass/_underscore-file-2"
+@import "../sass/underscore-file-2"
+@import "_underscore-file-2.scss"
+@import "underscore-file-2.scss"
+@import "./_underscore-file-2.scss"
+@import "./underscore-file-2.scss"
+@import "../sass/_underscore-file-2.scss"
+@import "../sass/underscore-file-2.scss"
+// CSS
+@import "_underscore-file-3"
+@import "underscore-file-3"
+@import "./_underscore-file-3"
+@import "./underscore-file-3"
+@import "../sass/_underscore-file-3"
+@import "../sass/underscore-file-3"
+// underscore index SASS
+@import "_underscore-dir"
+@import "./_underscore-dir"
+@import "../sass/_underscore-dir"
+@import "_underscore-dir/_index"
+@import "./_underscore-dir/_index"
+@import "../sass/_underscore-dir/_index"
+@import "_underscore-dir/_index.sass"
+@import "./_underscore-dir/_index.sass"
+@import "../sass/_underscore-dir/_index.sass"
+@import "_underscore-dir/index"
+@import "./_underscore-dir/index"
+@import "../sass/_underscore-dir/index"
+@import "_underscore-dir/index.sass"
+@import "./_underscore-dir/index.sass"
+@import "../sass/_underscore-dir/index.sass"
+// index SASS
+@import "_underscore-dir-1"
+@import "./_underscore-dir-1"
+@import "../sass/_underscore-dir-1"
+@import "_underscore-dir-1/index"
+@import "./_underscore-dir-1/index"
+@import "../sass/_underscore-dir-1/index"
+@import "_underscore-dir-1/index.sass"
+@import "./_underscore-dir-1/index.sass"
+@import "../sass/_underscore-dir-1/index.sass"
+// underscore index SCSS
+@import "_underscore-dir-2"
+@import "./_underscore-dir-2"
+@import "../sass/_underscore-dir-2"
+@import "_underscore-dir-2/_index"
+@import "./_underscore-dir-2/_index"
+@import "../sass/_underscore-dir-2/_index"
+@import "_underscore-dir-2/_index.scss"
+@import "./_underscore-dir-2/_index.scss"
+@import "../sass/_underscore-dir-2/_index.scss"
+@import "_underscore-dir-2/index"
+@import "./_underscore-dir-2/index"
+@import "../sass/_underscore-dir-2/index"
+@import "_underscore-dir-2/index.scss"
+@import "./_underscore-dir-2/index.scss"
+@import "../sass/_underscore-dir-2/index.scss"
+// index SCSS
+@import "_underscore-dir-3"
+@import "./_underscore-dir-3"
+@import "../sass/_underscore-dir-3"
+@import "_underscore-dir-3/index"
+@import "./_underscore-dir-3/index"
+@import "../sass/_underscore-dir-3/index"
+@import "_underscore-dir-3/index.scss"
+@import "./_underscore-dir-3/index.scss"
+@import "../sass/_underscore-dir-3/index.scss"
+// underscore index CSS
+@import "_underscore-dir-4"
+@import "./_underscore-dir-4"
+@import "../sass/_underscore-dir-4"
+@import "_underscore-dir-4/_index"
+@import "./_underscore-dir-4/_index"
+@import "../sass/_underscore-dir-4/_index"
+@import "_underscore-dir-4/index"
+@import "./_underscore-dir-4/index"
+@import "../sass/_underscore-dir-4/index"
+// index CSS
+@import "_underscore-dir-5"
+@import "./_underscore-dir-5"
+@import "../sass/_underscore-dir-5"
+@import "_underscore-dir-5/index"
+@import "./_underscore-dir-5/index"
+@import "../sass/_underscore-dir-5/index"
diff --git a/test/sass/import-without-extension-and-underscore.sass b/test/sass/import-without-extension-and-underscore.sass
new file mode 100644
index 00000000..bbf6e0fd
--- /dev/null
+++ b/test/sass/import-without-extension-and-underscore.sass
@@ -0,0 +1,75 @@
+// Filename
+@import "word"
+@import "./word"
+@import "../sass/word"
+@import "word-1"
+@import "./word-1"
+@import "../sass/word-1"
+@import "word-2"
+@import "./word-2"
+@import "../sass/word-2"
+@import "word-3"
+@import "./word-3"
+@import "../sass/word-3"
+@import "word-4"
+@import "./word-4"
+@import "../sass/word-4"
+@import "word-5"
+@import "./word-5"
+@import "../sass/word-5"
+@import "word-6"
+@import "./word-6"
+@import "../sass/word-6"
+@import "word-7"
+@import "./word-7"
+@import "../sass/word-7"
+@import "word-8"
+@import "./word-8"
+@import "../sass/word-8"
+@import "word-9"
+@import "./word-9"
+@import "../sass/word-9"
+@import "word-10"
+@import "./word-10"
+@import "../sass/word-10"
+@import "word-11"
+@import "./word-11"
+@import "../sass/word-11"
+// Directory/filename
+@import 'directory/file'
+@import './directory/file'
+@import '../sass/directory/file'
+@import 'directory-1/file'
+@import './directory-1/file'
+@import '../sass/directory-1/file'
+@import 'directory-2/file'
+@import './directory-2/file'
+@import '../sass/directory-2/file'
+@import 'directory-3/file'
+@import './directory-3/file'
+@import '../sass/directory-3/file'
+@import 'directory-4/file'
+@import './directory-4/file'
+@import '../sass/directory-4/file'
+@import 'directory-5/file'
+@import './directory-5/file'
+@import '../sass/directory-5/file'
+// Directory/filename with `_index` and `index`
+@import 'directory-6/file'
+@import './directory-6/file'
+@import '../sass/directory-6/file'
+@import 'directory-7/file'
+@import './directory-7/file'
+@import '../sass/directory-7/file'
+@import 'directory-8/file'
+@import './directory-8/file'
+@import '../sass/directory-8/file'
+@import 'directory-9/file'
+@import './directory-9/file'
+@import '../sass/directory-9/file'
+@import 'directory-10/file'
+@import './directory-10/file'
+@import '../sass/directory-10/file'
+@import 'directory-11/file'
+@import './directory-11/file'
+@import '../sass/directory-11/file'
diff --git a/test/sass/nested/_example-5.sass b/test/sass/nested/_example-5.sass
new file mode 100644
index 00000000..e91cac1a
--- /dev/null
+++ b/test/sass/nested/_example-5.sass
@@ -0,0 +1,2 @@
+.example-5
+  color: aquamarine
diff --git a/test/sass/nested/example-4.sass b/test/sass/nested/example-4.sass
new file mode 100644
index 00000000..83cd3d00
--- /dev/null
+++ b/test/sass/nested/example-4.sass
@@ -0,0 +1,2 @@
+.example-4
+  color: greenyellow
diff --git a/test/sass/nested/example-6.SASS b/test/sass/nested/example-6.SASS
new file mode 100644
index 00000000..944b7a35
--- /dev/null
+++ b/test/sass/nested/example-6.SASS
@@ -0,0 +1,2 @@
+.example-6
+  color: rosybrown
diff --git a/test/sass/spec/.gitignore b/test/sass/spec/.gitignore
deleted file mode 100644
index db8b4be7..00000000
--- a/test/sass/spec/.gitignore
+++ /dev/null
@@ -1,2 +0,0 @@
-# Will be populated by npm pretest
-*.css
diff --git a/test/sass/spec/dart-sass/.gitignore b/test/sass/spec/dart-sass/.gitignore
deleted file mode 100644
index db8b4be7..00000000
--- a/test/sass/spec/dart-sass/.gitignore
+++ /dev/null
@@ -1,2 +0,0 @@
-# Will be populated by npm pretest
-*.css
diff --git a/test/sass/spec/node-sass/.gitignore b/test/sass/spec/node-sass/.gitignore
deleted file mode 100644
index db8b4be7..00000000
--- a/test/sass/spec/node-sass/.gitignore
+++ /dev/null
@@ -1,2 +0,0 @@
-# Will be populated by npm pretest
-*.css
diff --git a/test/sass/word-10/_index.css b/test/sass/word-10/_index.css
new file mode 100644
index 00000000..142062d9
--- /dev/null
+++ b/test/sass/word-10/_index.css
@@ -0,0 +1,3 @@
+.word-10 {
+  color: #fff4c2;
+}
diff --git a/test/sass/word-11/index.css b/test/sass/word-11/index.css
new file mode 100644
index 00000000..a7d5ad57
--- /dev/null
+++ b/test/sass/word-11/index.css
@@ -0,0 +1,3 @@
+.word-11 {
+  color: #008800;
+}
diff --git a/test/sass/word-3.sass b/test/sass/word-3.sass
new file mode 100644
index 00000000..94c40d59
--- /dev/null
+++ b/test/sass/word-3.sass
@@ -0,0 +1,2 @@
+.word-3
+  color: #000088
diff --git a/test/sass/word-4.scss b/test/sass/word-4.scss
new file mode 100644
index 00000000..0082a21d
--- /dev/null
+++ b/test/sass/word-4.scss
@@ -0,0 +1,3 @@
+.word-4 {
+  color: #aaaaaa;
+}
diff --git a/test/sass/word-5.css b/test/sass/word-5.css
new file mode 100644
index 00000000..edc3fae0
--- /dev/null
+++ b/test/sass/word-5.css
@@ -0,0 +1,3 @@
+.word-5 {
+  color: fuchsia;
+}
diff --git a/test/sass/word-6/_index.sass b/test/sass/word-6/_index.sass
new file mode 100644
index 00000000..431a9cc1
--- /dev/null
+++ b/test/sass/word-6/_index.sass
@@ -0,0 +1,2 @@
+.word-6
+  color: azure
diff --git a/test/sass/word-7/index.sass b/test/sass/word-7/index.sass
new file mode 100644
index 00000000..a1e9fbac
--- /dev/null
+++ b/test/sass/word-7/index.sass
@@ -0,0 +1,2 @@
+.word-7
+  color: red
diff --git a/test/sass/word-8/_index.scss b/test/sass/word-8/_index.scss
new file mode 100644
index 00000000..3200bf43
--- /dev/null
+++ b/test/sass/word-8/_index.scss
@@ -0,0 +1,3 @@
+.word-8 {
+  color: moccasin;
+}
diff --git a/test/sass/word-9/index.scss b/test/sass/word-9/index.scss
new file mode 100644
index 00000000..baaf6318
--- /dev/null
+++ b/test/sass/word-9/index.scss
@@ -0,0 +1,3 @@
+.word-9 {
+  color: darkcyan;
+}
diff --git a/test/scss/_example-2.scss b/test/scss/_example-2.scss
new file mode 100644
index 00000000..8f9c8fca
--- /dev/null
+++ b/test/scss/_example-2.scss
@@ -0,0 +1,3 @@
+.example-2 {
+  color: blue;
+}
diff --git a/test/scss/_example-3.SCSS b/test/scss/_example-3.SCSS
new file mode 100644
index 00000000..2190cfac
--- /dev/null
+++ b/test/scss/_example-3.SCSS
@@ -0,0 +1,3 @@
+.example-2 {
+  color: black;
+}
diff --git a/test/scss/_underscore-dir-1/index.scss b/test/scss/_underscore-dir-1/index.scss
new file mode 100644
index 00000000..a0120041
--- /dev/null
+++ b/test/scss/_underscore-dir-1/index.scss
@@ -0,0 +1,3 @@
+.underscore-dir-1-index {
+  color: goldenrod;
+}
diff --git a/test/scss/_underscore-dir-2/_index.sass b/test/scss/_underscore-dir-2/_index.sass
new file mode 100644
index 00000000..829fb853
--- /dev/null
+++ b/test/scss/_underscore-dir-2/_index.sass
@@ -0,0 +1,2 @@
+.underscore-dir-2-index
+  color: mediumpurple
diff --git a/test/scss/_underscore-dir-3/index.sass b/test/scss/_underscore-dir-3/index.sass
new file mode 100644
index 00000000..3cc6baea
--- /dev/null
+++ b/test/scss/_underscore-dir-3/index.sass
@@ -0,0 +1,3 @@
+.underscore-dir-3-index
+  color: bisque
+
diff --git a/test/scss/_underscore-dir-4/_index.css b/test/scss/_underscore-dir-4/_index.css
new file mode 100644
index 00000000..fb53ce04
--- /dev/null
+++ b/test/scss/_underscore-dir-4/_index.css
@@ -0,0 +1,3 @@
+.underscore-dir-4-index {
+  color: maroon;
+}
diff --git a/test/scss/_underscore-dir-5/index.css b/test/scss/_underscore-dir-5/index.css
new file mode 100644
index 00000000..69c5ce54
--- /dev/null
+++ b/test/scss/_underscore-dir-5/index.css
@@ -0,0 +1,3 @@
+.underscore-dir-5-index {
+  color: magenta;
+}
diff --git a/test/scss/_underscore-dir/_index.scss b/test/scss/_underscore-dir/_index.scss
new file mode 100644
index 00000000..401661b4
--- /dev/null
+++ b/test/scss/_underscore-dir/_index.scss
@@ -0,0 +1,3 @@
+.underscore-dir-index {
+  color: goldenrod;
+}
diff --git a/test/scss/_underscore-file-1.scss b/test/scss/_underscore-file-1.scss
new file mode 100644
index 00000000..eea5f86f
--- /dev/null
+++ b/test/scss/_underscore-file-1.scss
@@ -0,0 +1,3 @@
+.underscore-1 {
+  color: cadetblue;
+}
diff --git a/test/scss/_underscore-file-2.sass b/test/scss/_underscore-file-2.sass
new file mode 100644
index 00000000..995046db
--- /dev/null
+++ b/test/scss/_underscore-file-2.sass
@@ -0,0 +1,2 @@
+.underscore-2
+  color: azure
diff --git a/test/scss/_underscore-file-3.css b/test/scss/_underscore-file-3.css
new file mode 100644
index 00000000..c7c32e7e
--- /dev/null
+++ b/test/scss/_underscore-file-3.css
@@ -0,0 +1,3 @@
+.underscore-3 {
+  color: chocolate;
+}
diff --git a/test/scss/_underscore-file.scss b/test/scss/_underscore-file.scss
new file mode 100644
index 00000000..47e4a109
--- /dev/null
+++ b/test/scss/_underscore-file.scss
@@ -0,0 +1,3 @@
+.underscore {
+  color: greenyellow;
+}
diff --git a/test/scss/_word-1.sass b/test/scss/_word-1.sass
new file mode 100644
index 00000000..80f6082c
--- /dev/null
+++ b/test/scss/_word-1.sass
@@ -0,0 +1,2 @@
+.word-1
+  color: black
diff --git a/test/scss/_word-2.css b/test/scss/_word-2.css
new file mode 100644
index 00000000..8d9432e7
--- /dev/null
+++ b/test/scss/_word-2.css
@@ -0,0 +1,3 @@
+.word-2 {
+  color: aquamarine;
+}
diff --git a/test/scss/_word.scss b/test/scss/_word.scss
new file mode 100644
index 00000000..878d700b
--- /dev/null
+++ b/test/scss/_word.scss
@@ -0,0 +1,3 @@
+.word {
+  color: red;
+}
diff --git a/test/scss/directory-1/file.scss b/test/scss/directory-1/file.scss
new file mode 100644
index 00000000..d8753682
--- /dev/null
+++ b/test/scss/directory-1/file.scss
@@ -0,0 +1,3 @@
+.directory-1-file {
+  color: #000066;
+}
diff --git a/test/scss/directory-10/file/_index.css b/test/scss/directory-10/file/_index.css
new file mode 100644
index 00000000..25209b13
--- /dev/null
+++ b/test/scss/directory-10/file/_index.css
@@ -0,0 +1,3 @@
+.directory-10-file {
+  color: #bbb;
+}
diff --git a/test/scss/directory-11/file/index.css b/test/scss/directory-11/file/index.css
new file mode 100644
index 00000000..39247396
--- /dev/null
+++ b/test/scss/directory-11/file/index.css
@@ -0,0 +1,3 @@
+.directory-10-file {
+  color: #ccb;
+}
diff --git a/test/scss/directory-2/_file.sass b/test/scss/directory-2/_file.sass
new file mode 100644
index 00000000..7e0a5410
--- /dev/null
+++ b/test/scss/directory-2/_file.sass
@@ -0,0 +1,2 @@
+.directory-2-file
+  color: #7f7f7f
diff --git a/test/scss/directory-3/file.sass b/test/scss/directory-3/file.sass
new file mode 100644
index 00000000..304e0699
--- /dev/null
+++ b/test/scss/directory-3/file.sass
@@ -0,0 +1,2 @@
+.directory-3-file
+  color: #7ff
diff --git a/test/scss/directory-4/_file.css b/test/scss/directory-4/_file.css
new file mode 100644
index 00000000..7de4a4db
--- /dev/null
+++ b/test/scss/directory-4/_file.css
@@ -0,0 +1,3 @@
+.directory-4-file {
+  color: #77ffff;
+}
diff --git a/test/scss/directory-5/file.css b/test/scss/directory-5/file.css
new file mode 100644
index 00000000..752d87b1
--- /dev/null
+++ b/test/scss/directory-5/file.css
@@ -0,0 +1,3 @@
+.directory-4-file {
+  color: #777;
+}
diff --git a/test/scss/directory-6/file/_index.scss b/test/scss/directory-6/file/_index.scss
new file mode 100644
index 00000000..1f7c60be
--- /dev/null
+++ b/test/scss/directory-6/file/_index.scss
@@ -0,0 +1,3 @@
+.directory-6-file {
+  color: #faf;
+}
diff --git a/test/scss/directory-7/file/index.scss b/test/scss/directory-7/file/index.scss
new file mode 100644
index 00000000..a2422990
--- /dev/null
+++ b/test/scss/directory-7/file/index.scss
@@ -0,0 +1,3 @@
+.directory-7-file {
+  color: #afa;
+}
diff --git a/test/scss/directory-8/file/_index.sass b/test/scss/directory-8/file/_index.sass
new file mode 100644
index 00000000..bede5b0d
--- /dev/null
+++ b/test/scss/directory-8/file/_index.sass
@@ -0,0 +1,2 @@
+.directory-8-file
+  color: #aaf
diff --git a/test/scss/directory-9/file/index.sass b/test/scss/directory-9/file/index.sass
new file mode 100644
index 00000000..0314d47b
--- /dev/null
+++ b/test/scss/directory-9/file/index.sass
@@ -0,0 +1,2 @@
+.directory-9-file
+  color: #ffa
diff --git a/test/scss/directory/_file.scss b/test/scss/directory/_file.scss
new file mode 100644
index 00000000..33dc9072
--- /dev/null
+++ b/test/scss/directory/_file.scss
@@ -0,0 +1,3 @@
+.directory-file {
+  color: #000066;
+}
diff --git a/test/scss/example-1.SCSS b/test/scss/example-1.SCSS
new file mode 100644
index 00000000..279069b4
--- /dev/null
+++ b/test/scss/example-1.SCSS
@@ -0,0 +1,3 @@
+.example-1 {
+  color: green;
+}
diff --git a/test/scss/example.scss b/test/scss/example.scss
new file mode 100644
index 00000000..f845c166
--- /dev/null
+++ b/test/scss/example.scss
@@ -0,0 +1,3 @@
+.example {
+  color: red;
+}
diff --git a/test/scss/import-_index.scss b/test/scss/import-_index.scss
new file mode 100644
index 00000000..38f76fed
--- /dev/null
+++ b/test/scss/import-_index.scss
@@ -0,0 +1 @@
+@import "~scss-package-with-underscore-index";
diff --git a/test/scss/import-with-extension.scss b/test/scss/import-with-extension.scss
new file mode 100644
index 00000000..4c27ba81
--- /dev/null
+++ b/test/scss/import-with-extension.scss
@@ -0,0 +1,18 @@
+@import "example.scss";
+@import "./example.scss";
+@import "../scss/example.scss";
+// TODO https://github.com/sass/dart-sass/issues/798#issuecomment-521229911
+// @import "example-1.SCSS";
+@import "example-2.scss";
+@import "./example-2.scss";
+@import "../scss/example-2.scss";
+// TODO https://github.com/sass/dart-sass/issues/798#issuecomment-521229911
+// @import "example-3.SCSS";
+@import "nested/example-4.scss";
+@import "./nested/example-4.scss";
+@import "../scss/nested/example-4.scss";
+@import "nested/example-5.scss";
+@import "./nested/example-5.scss";
+@import "../scss/nested/example-5.scss";
+// TODO https://github.com/sass/dart-sass/issues/798#issuecomment-521229911
+// @import "nested/example-6.SCSS";
diff --git a/test/scss/import-with-underscore.scss b/test/scss/import-with-underscore.scss
new file mode 100644
index 00000000..a148f4d1
--- /dev/null
+++ b/test/scss/import-with-underscore.scss
@@ -0,0 +1,112 @@
+@import "_underscore-file";
+@import "underscore-file";
+@import "./_underscore-file";
+@import "./underscore-file";
+@import "../scss/_underscore-file";
+@import "../scss/underscore-file";
+@import "_underscore-file.scss";
+@import "./_underscore-file.scss";
+@import "../scss/_underscore-file.scss";
+@import "../scss/underscore-file.scss";
+// SCSS
+@import "_underscore-file-1";
+@import "underscore-file-1";
+@import "./_underscore-file-1";
+@import "./underscore-file-1";
+@import "../scss/_underscore-file-1";
+@import "../scss/underscore-file-1";
+@import "_underscore-file-1.scss";
+@import "underscore-file-1.scss";
+@import "./_underscore-file-1.scss";
+@import "./underscore-file-1.scss";
+@import "../scss/_underscore-file-1.scss";
+@import "../scss/underscore-file-1.scss";
+// SASS
+@import "_underscore-file-2";
+@import "underscore-file-2";
+@import "./_underscore-file-2";
+@import "./underscore-file-2";
+@import "../scss/_underscore-file-2";
+@import "../scss/underscore-file-2";
+@import "_underscore-file-2.sass";
+@import "underscore-file-2.sass";
+@import "./_underscore-file-2.sass";
+@import "./underscore-file-2.sass";
+@import "../scss/_underscore-file-2.sass";
+@import "../scss/underscore-file-2.sass";
+// CSS
+@import "_underscore-file-3";
+@import "underscore-file-3";
+@import "./_underscore-file-3";
+@import "./underscore-file-3";
+@import "../scss/_underscore-file-3";
+@import "../scss/underscore-file-3";
+// underscore index SCSS
+@import "_underscore-dir";
+@import "./_underscore-dir";
+@import "../scss/_underscore-dir";
+@import "_underscore-dir/_index";
+@import "./_underscore-dir/_index";
+@import "../scss/_underscore-dir/_index";
+@import "_underscore-dir/_index.scss";
+@import "./_underscore-dir/_index.scss";
+@import "../scss/_underscore-dir/_index.scss";
+@import "_underscore-dir/index";
+@import "./_underscore-dir/index";
+@import "../scss/_underscore-dir/index";
+@import "_underscore-dir/index.scss";
+@import "./_underscore-dir/index.scss";
+@import "../scss/_underscore-dir/index.scss";
+// index SCSS
+@import "_underscore-dir-1";
+@import "./_underscore-dir-1";
+@import "../scss/_underscore-dir-1";
+@import "_underscore-dir-1/index";
+@import "./_underscore-dir-1/index";
+@import "../scss/_underscore-dir-1/index";
+@import "_underscore-dir-1/index.scss";
+@import "./_underscore-dir-1/index.scss";
+@import "../scss/_underscore-dir-1/index.scss";
+// underscore index SASS
+@import "_underscore-dir-2";
+@import "./_underscore-dir-2";
+@import "../scss/_underscore-dir-2";
+@import "_underscore-dir-2/_index";
+@import "./_underscore-dir-2/_index";
+@import "../scss/_underscore-dir-2/_index";
+@import "_underscore-dir-2/_index.sass";
+@import "./_underscore-dir-2/_index.sass";
+@import "../scss/_underscore-dir-2/_index.sass";
+@import "_underscore-dir-2/index";
+@import "./_underscore-dir-2/index";
+@import "../scss/_underscore-dir-2/index";
+@import "_underscore-dir-2/index.sass";
+@import "./_underscore-dir-2/index.sass";
+@import "../scss/_underscore-dir-2/index.sass";
+// index SASS
+@import "_underscore-dir-3";
+@import "./_underscore-dir-3";
+@import "../scss/_underscore-dir-3";
+@import "_underscore-dir-3/index";
+@import "./_underscore-dir-3/index";
+@import "../scss/_underscore-dir-3/index";
+@import "_underscore-dir-3/index.sass";
+@import "./_underscore-dir-3/index.sass";
+@import "../scss/_underscore-dir-3/index.sass";
+// underscore index CSS
+@import "_underscore-dir-4";
+@import "./_underscore-dir-4";
+@import "../scss/_underscore-dir-4";
+@import "_underscore-dir-4/_index";
+@import "./_underscore-dir-4/_index";
+@import "../scss/_underscore-dir-4/_index";
+@import "_underscore-dir-4/index";
+@import "./_underscore-dir-4/index";
+@import "../scss/_underscore-dir-4/index";
+// index CSS
+@import "_underscore-dir-5";
+@import "./_underscore-dir-5";
+@import "../scss/_underscore-dir-5";
+@import "_underscore-dir-5/index";
+@import "./_underscore-dir-5/index";
+@import "../scss/_underscore-dir-5/index";
diff --git a/test/scss/import-without-extension-and-underscore.scss b/test/scss/import-without-extension-and-underscore.scss
new file mode 100644
index 00000000..eced83b6
--- /dev/null
+++ b/test/scss/import-without-extension-and-underscore.scss
@@ -0,0 +1,75 @@
+// Filename
+@import "word";
+@import "./word";
+@import "../scss/word";
+@import "word-1";
+@import "./word-1";
+@import "../scss/word-1";
+@import "word-2";
+@import "./word-2";
+@import "../scss/word-2";
+@import "word-3";
+@import "./word-3";
+@import "../scss/word-3";
+@import "word-4";
+@import "./word-4";
+@import "../scss/word-4";
+@import "word-5";
+@import "./word-5";
+@import "../scss/word-5";
+@import "word-6";
+@import "./word-6";
+@import "../scss/word-6";
+@import "word-7";
+@import "./word-7";
+@import "../scss/word-7";
+@import "word-8";
+@import "./word-8";
+@import "../scss/word-8";
+@import "word-9";
+@import "./word-9";
+@import "../scss/word-9";
+@import "word-10";
+@import "./word-10";
+@import "../scss/word-10";
+@import "word-11";
+@import "./word-11";
+@import "../scss/word-11";
+// Directory/filename
+@import 'directory/file';
+@import './directory/file';
+@import '../scss/directory/file';
+@import 'directory-1/file';
+@import './directory-1/file';
+@import '../scss/directory-1/file';
+@import 'directory-2/file';
+@import './directory-2/file';
+@import '../scss/directory-2/file';
+@import 'directory-3/file';
+@import './directory-3/file';
+@import '../scss/directory-3/file';
+@import 'directory-4/file';
+@import './directory-4/file';
+@import '../scss/directory-4/file';
+@import 'directory-5/file';
+@import './directory-5/file';
+@import '../scss/directory-5/file';
+// Directory/filename with `_index` and `index`
+@import 'directory-6/file';
+@import './directory-6/file';
+@import '../scss/directory-6/file';
+@import 'directory-7/file';
+@import './directory-7/file';
+@import '../scss/directory-7/file';
+@import 'directory-8/file';
+@import './directory-8/file';
+@import '../scss/directory-8/file';
+@import 'directory-9/file';
+@import './directory-9/file';
+@import '../scss/directory-9/file';
+@import 'directory-10/file';
+@import './directory-10/file';
+@import '../scss/directory-10/file';
+@import 'directory-11/file';
+@import './directory-11/file';
+@import '../scss/directory-11/file';
diff --git a/test/scss/nested/_example-5.scss b/test/scss/nested/_example-5.scss
new file mode 100644
index 00000000..8775f80f
--- /dev/null
+++ b/test/scss/nested/_example-5.scss
@@ -0,0 +1,3 @@
+.example-5 {
+  color: aquamarine;
+}
diff --git a/test/scss/nested/example-4.scss b/test/scss/nested/example-4.scss
new file mode 100644
index 00000000..956bb30d
--- /dev/null
+++ b/test/scss/nested/example-4.scss
@@ -0,0 +1,3 @@
+.example-4 {
+  color: greenyellow;
+}
diff --git a/test/scss/nested/example-6.SCSS b/test/scss/nested/example-6.SCSS
new file mode 100644
index 00000000..5f08cafc
--- /dev/null
+++ b/test/scss/nested/example-6.SCSS
@@ -0,0 +1,3 @@
+.example-6 {
+  color: rosybrown;
+}
diff --git a/test/scss/spec/.gitignore b/test/scss/spec/.gitignore
deleted file mode 100644
index db8b4be7..00000000
--- a/test/scss/spec/.gitignore
+++ /dev/null
@@ -1,2 +0,0 @@
-# Will be populated by npm pretest
-*.css
diff --git a/test/scss/spec/dart-sass/.gitignore b/test/scss/spec/dart-sass/.gitignore
deleted file mode 100644
index db8b4be7..00000000
--- a/test/scss/spec/dart-sass/.gitignore
+++ /dev/null
@@ -1,2 +0,0 @@
-# Will be populated by npm pretest
-*.css
diff --git a/test/scss/spec/node-sass/.gitignore b/test/scss/spec/node-sass/.gitignore
deleted file mode 100644
index db8b4be7..00000000
--- a/test/scss/spec/node-sass/.gitignore
+++ /dev/null
@@ -1,2 +0,0 @@
-# Will be populated by npm pretest
-*.css
diff --git a/test/scss/word-10/_index.css b/test/scss/word-10/_index.css
new file mode 100644
index 00000000..142062d9
--- /dev/null
+++ b/test/scss/word-10/_index.css
@@ -0,0 +1,3 @@
+.word-10 {
+  color: #fff4c2;
+}
diff --git a/test/scss/word-11/index.css b/test/scss/word-11/index.css
new file mode 100644
index 00000000..a7d5ad57
--- /dev/null
+++ b/test/scss/word-11/index.css
@@ -0,0 +1,3 @@
+.word-11 {
+  color: #008800;
+}
diff --git a/test/scss/word-3.scss b/test/scss/word-3.scss
new file mode 100644
index 00000000..837f7eae
--- /dev/null
+++ b/test/scss/word-3.scss
@@ -0,0 +1,3 @@
+.word-3 {
+  color: #000088;
+}
diff --git a/test/scss/word-4.sass b/test/scss/word-4.sass
new file mode 100644
index 00000000..500f8051
--- /dev/null
+++ b/test/scss/word-4.sass
@@ -0,0 +1,2 @@
+.word-4
+  color: #aaaaaa
diff --git a/test/scss/word-5.css b/test/scss/word-5.css
new file mode 100644
index 00000000..edc3fae0
--- /dev/null
+++ b/test/scss/word-5.css
@@ -0,0 +1,3 @@
+.word-5 {
+  color: fuchsia;
+}
diff --git a/test/scss/word-6/_index.scss b/test/scss/word-6/_index.scss
new file mode 100644
index 00000000..5421c31e
--- /dev/null
+++ b/test/scss/word-6/_index.scss
@@ -0,0 +1,3 @@
+.word-6 {
+  color: azure;
+}
diff --git a/test/scss/word-7/index.scss b/test/scss/word-7/index.scss
new file mode 100644
index 00000000..b74b592b
--- /dev/null
+++ b/test/scss/word-7/index.scss
@@ -0,0 +1,3 @@
+.word-7 {
+  color: red;
+}
diff --git a/test/scss/word-8/_index.sass b/test/scss/word-8/_index.sass
new file mode 100644
index 00000000..95cfd5e1
--- /dev/null
+++ b/test/scss/word-8/_index.sass
@@ -0,0 +1,2 @@
+.word-8
+  color: moccasin
diff --git a/test/scss/word-9/index.sass b/test/scss/word-9/index.sass
new file mode 100644
index 00000000..9233dd61
--- /dev/null
+++ b/test/scss/word-9/index.sass
@@ -0,0 +1,2 @@
+.word-9
+  color: darkcyan