feat(testing): Implement "assertSnapshot"

testing/asserts.ts

@@ -12,6 +12,8 @@ import {
   stripColor,
   white,
 } from "../fmt/colors.ts";
+import { fromFileUrl, parse, join } from "../path/mod.ts";
+import { ensureFile, ensureFileSync } from "../fs/mod.ts";
 import { diff, DiffResult, diffstr, DiffType } from "./_diff.ts";
 
 const CAN_NOT_DISPLAY = "[Cannot display]";
@@ -864,3 +866,59 @@ export function unimplemented(msg?: string): never {
 export function unreachable(): never {
   throw new AssertionError("unreachable");
 }
+
+let snapshotFile: Record<string, unknown> | undefined = undefined;
+const updatedSnapshotFile: Record<string, unknown> = {};
+// const snapshotMap: Record<string, number> = {};
+
+export async function assertSnapshot(context: Deno.TestContext, actual: unknown) {
+  const name = getName(context);
+  // const count = getCount(name);
+
+  if (!snapshotFile) {
+    const snapshotPath = getSnapshotPath();
+    await ensureFile(snapshotPath);
+    const file = await Deno.readTextFile(snapshotPath);
+    snapshotFile = file ? JSON.parse(file) : {};
+  }
+  const snapshot = snapshotFile?.[name];
+  if (!Deno.args.includes('--update')) {
+    assertEquals(actual, snapshot);
+  } else {
+    let isEqual = true;
+    try {
+      assertEquals(actual, snapshot);
+    } catch {
+      isEqual = false;
+    }
+    if (!isEqual) console.info("Snapshot updated", name);
+  }
+  updatedSnapshotFile[name] = actual;
+
+  globalThis.onunload = writeSnapshotFileSync;
+
+  // function getCount() {
+  //   const count = snapshotMap?.[name] ? snapshotMap[name] : 1;
+  //   snapshotMap[name] = count + 1;
+  //   return count;
+  // }
+
+  function getName(context: Deno.TestContext): string {
+    if (context.parent) return `${getName(context.parent)} > ${context.name}`;
+    return context.name;
+  }
+
+  function getSnapshotPath() {
+    const testFile = fromFileUrl(context.origin);
+    const parts = parse(testFile);
+    return `${join(parts.dir, parts.name)}.snap`;
+  }
+
+  function writeSnapshotFileSync() {
+    const snapshotPath = getSnapshotPath();
+    ensureFileSync(snapshotPath);
+    const file = JSON.stringify(updatedSnapshotFile, null, 2);
+    Deno.writeTextFileSync(snapshotPath, file);
+    console.log('Snapshot updated!');
+  }
+}

testing/asserts_test.snap

@@ -0,0 +1,14 @@
+{
+  "Snapshot Test": {
+    "a": 1,
+    "b": 2
+  },
+  "Snapshot Test > babo": {
+    "b": 2,
+    "c": 3
+  },
+  "Snapshot Test > babo > merong": {
+    "b": 2,
+    "c": 4
+  }
+}

testing/asserts_test.ts

@@ -15,6 +15,7 @@ import {
   assertNotStrictEquals,
   assertObjectMatch,
   assertRejects,
+  assertSnapshot,
   assertStrictEquals,
   assertStringIncludes,
   assertThrows,
@@ -1408,3 +1409,13 @@ Deno.test("Assert Is Error with custom Error", () => {
     'Expected error to be instance of "CustomError", but was "AnotherCustomError".',
   );
 });
+
+Deno.test("Snapshot Test", async (t) => {
+  await assertSnapshot(t, { a: 1, b: 2 });
+  await t.step("babo", async (t) => {
+    await assertSnapshot(t, { b: 2, c: 3 });
+    await t.step("merong", async (t) => {
+      await assertSnapshot(t, { b: 2, c: 4 });
+    });
+  });
+});