test: do not write fixture in test-require-symlink

test-require-symlink modifies the fixture directory by adding a symlink.
Copy the fixture to the test tmpdir instead of modifying the fixture
directory.

This also uses a more empirical test for checking for the ability to
make symlinks on Windows.

test/fixtures/module-require-symlink/symlinked.js

@@ -1,11 +1,12 @@
 'use strict';
 const assert = require('assert');
+const path = require('path');
+
 const foo = require('./foo');
-const fixtures = require('../../common/fixtures');
 
-const linkScriptTarget = fixtures.path('module-require-symlink', 'symlinked.js');
+const linkScriptEnding = path.join('module-require-symlink', 'symlinked.js');
 
 assert.strictEqual(foo.dep1.bar.version, 'CORRECT_VERSION');
 assert.strictEqual(foo.dep2.bar.version, 'CORRECT_VERSION');
-assert.strictEqual(__filename, linkScriptTarget);
+assert(__filename.endsWith(linkScriptEnding));
 assert(__filename in require.cache);

test/parallel/test-require-symlink.js

@@ -1,52 +1,66 @@
 // Flags: --preserve-symlinks
 'use strict';
 const common = require('../common');
+
+if (!common.canCreateSymLink())
+  common.skip('insufficient privileges');
+
 const assert = require('assert');
-const path = require('path');
+const { spawn } = require('child_process');
 const fs = require('fs');
-const { exec, spawn } = require('child_process');
+const path = require('path');
+const process = require('process');
+
+// Setup: Copy fixtures to tmp directory.
+
 const fixtures = require('../common/fixtures');
+const dirName = 'module-require-symlink';
+const fixtureSource = fixtures.path(dirName);
+const tmpDirTarget = path.join(common.tmpDir, dirName);
 
+// Copy fixtureSource to linkTarget recursively.
 common.refreshTmpDir();
 
-const linkTarget = fixtures.path('module-require-symlink',
-                                 'node_modules',
-                                 'dep2');
+function copyDir(source, target) {
+  fs.mkdirSync(target);
+  fs.readdirSync(source).forEach((entry) => {
+    const fullPathSource = path.join(source, entry);
+    const fullPathTarget = path.join(target, entry);
+    const stats = fs.statSync(fullPathSource);
+    if (stats.isDirectory()) {
+      copyDir(fullPathSource, fullPathTarget);
+    } else {
+      fs.copyFileSync(fullPathSource, fullPathTarget);
+    }
+  });
+}
+
+copyDir(fixtureSource, tmpDirTarget);
 
-const linkDir = fixtures.path('module-require-symlink',
-                              'node_modules',
-                              'dep1',
-                              'node_modules',
-                              'dep2');
+// Move to tmp dir and do everything with relative paths there so that the test
+// doesn't incorrectly fail due to a symlink somewhere else in the absolte path.
+process.chdir(common.tmpDir);
 
-const linkScriptTarget = fixtures.path('module-require-symlink',
-                                       'symlinked.js');
+const linkDir = path.join(dirName,
+                          'node_modules',
+                          'dep1',
+                          'node_modules',
+                          'dep2');
 
-const linkScript = path.join(common.tmpDir, 'module-require-symlink.js');
+const linkTarget = path.join('..', '..', 'dep2');
 
-if (common.isWindows) {
-  // On Windows, creating symlinks requires admin privileges.
-  // We'll only try to run symlink test if we have enough privileges.
-  exec('whoami /priv', function(err, o) {
-    if (err || !o.includes('SeCreateSymbolicLinkPrivilege'))
-      common.skip('insufficient privileges');
+const linkScript = 'linkscript.js';
 
-    test();
-  });
-} else {
-  test();
-}
+const linkScriptTarget = path.join(dirName, 'symlinked.js');
 
-function test() {
-  process.on('exit', function() {
-    fs.unlinkSync(linkDir);
-  });
+test();
 
+function test() {
   fs.symlinkSync(linkTarget, linkDir);
   fs.symlinkSync(linkScriptTarget, linkScript);
 
   // load symlinked-module
-  const fooModule = require(fixtures.path('/module-require-symlink/foo.js'));
+  const fooModule = require(path.join(tmpDirTarget, 'foo.js'));
   assert.strictEqual(fooModule.dep1.bar.version, 'CORRECT_VERSION');
   assert.strictEqual(fooModule.dep2.bar.version, 'CORRECT_VERSION');