Add API Tests

Skill: Add TypeScript API Tests

Every change under src/ belongs in the Jest suites at packages/react-native-executorch/__tests__/. They run on a laptop or a CI runner — no simulator, no device, no .pte — and finish in a few seconds.

yarn workspace react-native-executorch test
yarn workspace react-native-executorch test __tests__/tasks   # one directory
yarn workspace react-native-executorch test -u                # update snapshots

Types come along for free: yarn typecheck already covers __tests__/.

🧩 The Fake Native Runtime

There is no stubbing of individual JSI calls. __tests__/support/fakeJsi.ts implements the whole __rnexecutorch_jsi__ contract in JavaScript — tensors hold real data, math/cv/speech operators compute real values — so a task pipeline runs end to end and its own logic is what the assertions measure.

A test describes the model it wants, then drives the real pipeline:

import { f32, method } from '../../src/core/schema';
import { fakeJsi } from '../support/fakeJsi';
import { tracked } from '../support/lifetime';
import { STRETCH_PREPROCESSING, exported, imageBuffer, writesOutputs } from '../support/fixtures';

fakeJsi.registerModel('/models/task.pte', {
  schema: exported(method('forward', [f32(1, 3, 4, 4)], [f32(1, 3)])),
  execute: writesOutputs([1, 0, 2]),
});

const runner = tracked(await createMyTask({ modelPath: '/models/task.pte', modelOpts }));
expect(await runner.runTask(imageBuffer(8, 8))).toEqual(/* ... */);

Key helpers:

🧠 What to Cover for a New Task Pipeline

1. Schema acceptance — one test per variant the pipeline declares (batched, unbatched, ...), asserting the factory resolves.
2. Schema rejection — a model that matches no variant, asserting the error names the mismatch (Rank mismatch, inconsistent bindings, ...). A caller should learn what is wrong from the message.
3. Configuration mismatch — e.g. a labels array that disagrees with the model's output dimension.
4. Postprocessing — the part that is yours: sorting, thresholding, suppression, colormaps, coordinate scaling. Choose fixture values that make the expected output obvious in the test.
5. Options — every default in modelOpts, and every per-call override.
6. Disposal — dispose() leaves fakeJsi.liveTensors() at 0 and fakeJsi.liveModels() empty, and repeated calls do not accumulate scratch tensors. The same has to hold when construction fails: allocate through a createResourceScope() and wrap the factory body in try/catch so a schema mismatch releases the model instead of stranding it. Add the factory to __tests__/tasks/constructionFailure.test.ts, which drives every one of them.
7. Sync/async parity — runTaskWorklet(x) equals await runTask(x).

Only the weights are out of scope, not the pipeline that runs on them. Before settling for schema-acceptance-and-disposal, check what is actually TypeScript: a decode loop, a sliding window, a chunker, an argument check, a streaming generator and a disposal path all run fine over a scripted execute. Reach for the minimal treatment only when the assertion would be measuring the fixture.

For a new hook, add a case to __tests__/hooks/: not-ready before the download lands, methods exposed after, errors surfaced through the shared error field, and every native handle released on unmount.

🔒 Leak Checking

Native memory is not garbage collected, so the setup file asserts after every test that nothing allocated through the fake was left undisposed. That gives each pipeline suite disposal coverage for free.

• Wrap construction in tracked() — it disposes at the end of the test and stops a failing assertion from cascading into a second, misleading error.
• A test that deliberately leaks calls allowNativeLeaks() with a comment saying why.

📐 Source-Level Conventions

__tests__/api/workletDirective.test.ts parses src/ with the TypeScript compiler and enforces the conventions no type can express:

• every exported function that calls into rnexecutorchJsi starts with 'worklet';
• no async function is marked as a worklet
• only src/native/bridge.ts names the __rnexecutorch_jsi__ global
• core/ never imports from extensions/, and hooks/ never imports from native/

If you add a new native wrapper without the directive, that suite fails — add the directive rather than the exception.

📋 Verification Checklist

When adding or changing code under src/, verify that:

• yarn workspace react-native-executorch test passes.
• A new task pipeline has a suite covering acceptance, rejection, postprocessing, options and disposal.
• A new hook has a lifecycle case in __tests__/hooks/.
• A new registry entry passes __tests__/api/modelRegistry.test.ts without the rules being loosened (https URL, pinned revision, modelname_backend_precision.pte, a folder naming that backend, and a DEFAULT that is one of the configs the group offers).
• A new error code is in VALID_ERROR_CODES, so isRnExecuTorchError does not reject the library's own error — __tests__/core/error.test.ts reads every code src/ raises out of the source and checks it is listed.
• A new export is reflected in the api/apiSurface snapshot, and the change is intentional (a removal or rename is a breaking change).
• Any new fake behavior in __tests__/support/ is faithful where fidelity changes an assertion, and its simplifications are commented.
• A new create<Task> allocates through createResourceScope() and is listed in __tests__/tasks/constructionFailure.test.ts.
• No test was made to pass by calling allowNativeLeaks(). Nothing in the suite needs it today, so reach for it only when a leak is genuinely the point of the test, and say why.