test(linters): forbid file-based snapshot matchers (#45661)

* test(linters): forbid file-based snapshot matchers

* test(linters): drop inline snapshot recommendation

* test(linters): assert on relevant sections instead of full bodies

.oxlintrc.json

@@ -190,6 +190,16 @@
       { "assertFunctionNames": ["expect", "expectTypeOf", "checkKeysSorted"] }
     ],
     "vitest/no-conditional-expect": "error",
+    "vitest/no-restricted-matchers": [
+      "error",
+      {
+        "toMatchSnapshot": "Use explicit assertions such as toEqual, toMatchObject or toBe so the expected value stays visible in the test file.",
+        "toThrowErrorMatchingSnapshot": "Use toThrow with the expected message.",
+        "rejects.toThrowErrorMatchingSnapshot": "Use rejects.toThrow with the expected message.",
+        "resolves.toMatchSnapshot": "Use explicit assertions such as resolves.toEqual or resolves.toMatchObject so the expected value stays visible in the test file.",
+        "toMatchFileSnapshot": "Use explicit assertions such as toEqual, toMatchObject or toBe so the expected value stays visible in the test file."
+      }
+    ],
     "vitest/no-standalone-expect": "error",
     "vitest/prefer-snapshot-hint": "error",
     "vitest/require-to-throw-message": "error"

docs/development/best-practices.md

@@ -292,9 +292,9 @@ if (end) {
   - `mockDeep` returns a mock for any property access, so typos in mocked names won't fail the test
 - Prefer `toEqual`
 - Use `toMatchObject` for huge objects when only parts need to be tested
-- Avoid `toMatchSnapshot`, only use it for:
-  - huge strings like the Renovate PR body text
-  - huge complex objects where you only need to test parts
+- Do not use snapshot matchers (`toMatchSnapshot`, `toMatchInlineSnapshot`, `toThrowErrorMatchingSnapshot`), write explicit assertions instead
+  - For huge strings like the Renovate PR body text, assert on the sections the test is about with `toContain`, `toStartWith` or `toEndWith`; compare the whole string with `toBe` only when producing exactly that text is the point of the test
+  - For huge complex objects where you only need to test parts, use `toMatchObject`
 - Avoid exporting functions purely for the purpose of testing unless you really need to
 - Avoid cast or prefer `x as T` instead of `<T>x` cast
   - Use `partial<T>()` from `test/util` if only a partial object is required