fix(jest): keep mocked hooks working after jest.resetAllMocks()

[giaBaoJS]

Fixes #551

@jacobp100 said in the issue:

A PR would be helpful if anyone wants to

Nobody has picked it up since, so here it is.

The problem

src/jest/mock.tsx wraps the two hooks in jest.fn(...) (added in #449) so tests can override them:

useSafeAreaInsets: jest.fn(() => { ... }),
useSafeAreaFrame: jest.fn(() => { ... }),

jest.resetAllMocks() removes the implementation from every mock function. Apps commonly call it from a global beforeEach/afterEach, and after that both hooks return undefined, so any component reading insets.top or frame.width throws:

TypeError: Cannot read properties of undefined (reading 'top')

This matches what @adamgeorgsson and @eppisapiafsl reported: the first test in a suite passes and every one after it fails. The current workarounds are patching the package to revert #449, or switching to jest.clearAllMocks() — which is not equivalent, and consumers should not have to know this.

The fix

Wrap the hooks in a Proxy that reinstalls the default implementation when getMockImplementation() reports it was stripped:

function mockHook<T extends (...args: never[]) => unknown>(implementation: T) {
  const hook = jest.fn(implementation);
  return new Proxy(hook, {
    apply(target, thisArg, args) {
      if (target.getMockImplementation() == null) {
        target.mockImplementation(implementation);
      }
      return Reflect.apply(target, thisArg, args);
    },
  });
}

mockReturnValue/mockImplementation set an implementation, so getMockImplementation() is non-null and the default is not reinstalled — overrides still win. Call tracking is untouched, since the proxy forwards to the same mock function.

This keeps the #449 behaviour (the hooks remain overridable jest.fns) rather than reverting it.

What I verified

Everything below was run locally on this branch, not inferred.

The defect reproduces on current main (f65d4d9, v5.9.0). The new test renders a component through jest.mock('react-native-safe-area-context', () => mockSafeAreaContext) — the exact setup the README prescribes — with jest.resetAllMocks() in a beforeEach. On unmodified main all three cases fail with TypeError: Cannot read properties of undefined (reading 'top' / 'width'). Removing only the jest.resetAllMocks() line makes them pass on unmodified main, which isolates the cause to the reset.

Counterfactual. With the test in place and src/jest/mock.tsx reverted to main: 3 failed. With the fix applied: 3 passed.

The two things people rely on still work, asserted in the test rather than argued:

• jest.mocked(useSafeAreaInsets).mockReturnValue(...) after a reset still wins over the reinstated default (useSafeAreaFrame in the same render falls back to the default, so one assertion covers both paths).
• toHaveBeenCalledTimes(1) on both hooks still holds after a reset.

No public type change. I built lib/typescript before and after the fix and diffed the generated jest/mock.d.ts — byte identical. Both hooks are still Mock<() => EdgeInsets> / Mock<() => Rect>.

Suite. yarn validate:jest goes from 4 suites / 21 tests to 5 suites / 24 tests, all passing, 11 snapshots unchanged. yarn format:prettier:check, yarn validate:eslint (still the same 3 pre-existing no-deep-imports warnings, none new) and yarn validate:typescript all pass.

Jest 30. I checked the fix against jest@30.4.2 in a scratch project. jest.fn(impl) still returns undefined after resetAllMocks() there, so the bug is not fixed upstream, and the proxied version returns the default, honours mockReturnValue, and stays jest.isMockFunction-true.

Packaging. npm pack --dry-run confirms the new src/jest/__tests__/ directory is excluded from the tarball by the existing !**/__tests__ entry in files.

What I could not verify

yarn test also runs format:clang:check and format:spotless:check. clang-format could not run on my machine — the bundled node_modules/clang-format/bin/darwin_x64/clang-format is an x86_64 binary and fails with spawn Unknown system error -86 on Apple Silicon. It fails identically on a clean checkout with zero changes, and this PR touches no .h/.cpp/.m/.mm/.java/.kt files, so neither native formatter is affected. CI runs on ubuntu-latest, where both should run normally.