See it work

The rule: a change is done when you have SEEN it work, not when a test passes. Tests prove behaviour. Only a screen proves layout. Never say "fixed" or "done" for something a person will see until you have looked at it, and never claim more than the layer you used can prove.

Read references/layers.md for how to run each layer. Read references/simulator-gotchas.md before trusting any simulator result. Read references/paid-tier-testing.md when the change touches a paywall, a usage limit or anything that differs between free and paid.

What you can and cannot use here

Check this first. It decides which layers are open to you.

Where you are running	Layers available
A Mac with Xcode and a simulator (or an Android emulator)	All of them
Linux or Windows with an Android emulator	Component tests, Android screenshots, Android smoke and journeys
A cloud session (no simulator, no emulator)	Component tests and the browser preview only

For a website (Platforms says web only), skip the simulator layers and use the web section near the end of this file instead.

Simulators need a Mac. A cloud session cannot see a phone screen at all. If the change needs a layer you do not have, do what you can, then say plainly which check is still owed and add it to the release checklist for a person to do on a device. Do not quietly downgrade the claim.

1. Decide which layer proves this change

Find the row that matches the change. Most changes need two layers: a test for the behaviour and a screen for the look.

The change	Prove it with
Logic, state, what renders in each case, what a tap does	Component test (layer 1)
Copy, colour, spacing, alignment, clipping, safe areas, anything you would describe by how it looks	Seeded screenshot (layer 2). Browser preview (layer 5) only for copy and colour, and only when there is no simulator
A new screen or route	Component test, plus a smoke case and its anchor (layer 3)
Navigation: "tapping X takes you to Y"	Component test that asserts the destination, plus a journey (layer 6) if the path crosses screens
Something that only breaks in a store build (native modules, minification, crash reporting)	Release build smoke run (layer 4)
A deep link, a share sheet, a paywall, onboarding	Journey from the real entry point (layer 6). A seeded jump cannot prove how you got there
A bug a user reported	Reproduce it first on the same OS version they have, then prove the fix the same way

2. Write the test first and watch it fail

For any behaviour change, write or update the component test before the code.

1. Write the test. Assert what a person sees:
   • the full string, not a fragment (a full string match is what catches clipped or truncated text),
   • every branch: loading, empty, success and error,
   • that a press does what it should,
   • the navigation destination, not just that a navigation call happened.
2. Run it and watch it fail for the right reason.
3. Make the change. Run it until it passes.
4. Undo the fix and confirm the test fails again. Then put the fix back. A test that passes with and without the fix proves nothing. This has caught navigation "fixes" whose tests passed either way.

If the project has the test after edit hook (templates/ui-test-hook.sh), the matching test runs after every UI edit and you will be told when a screen has no test. Act on that message; do not work around it.

3. Look at it

For anything visual, get a screenshot of the real screen in the real state and read the image yourself before saying anything about it.

• On a Mac: fire the test only seed deep link for the screen (<your-scheme>://test-seed?screen=<id>), let it settle, take a simulator screenshot, and open the PNG. See layer 2 in references/layers.md.
• Check the screenshot is of YOUR app and YOUR code. A shared simulator often has other apps installed, and one may be in front, or a system dialog may cover the screen. Then check the copy, build and worktree: a stale bundle or a Metro serving another checkout fakes a pass. See references/simulator-gotchas.md.
• If the bug is about layout near headers, modals or safe areas, use a simulator on the same major OS version as the person who reported it.
• In a cloud session: use the browser preview (layer 5). Say in the same message that it cannot prove geometry, gestures or anything native.

Compare against what was asked. If it is not right, fix and look again. Do not describe a screen you have not seen.

4. Run the wider checks the change calls for

• New or renamed screen: add its testID="screen-<id>" anchor on every top level branch, add a smoke case, and run the coverage check (templates/check-e2e-coverage.mjs). Then run that one case.
• Before a release: run the whole smoke tier on both platforms against a release build made with the E2E flag (layer 4). Build the store binary again WITHOUT the flag afterwards. The test seam must never be in a store build.
• A journey changed: run the journey flow from the real entry point.

5. Show the evidence

Finish with what was proved and how, in a few lines:

• Which layer, which command, and the result (pass counts, or the screenshot itself shown to the user).
• That the test failed with the fix undone, for a bug fix.
• What is still unproved and why (no simulator, no real device, camera, purchase flow, other OS version). Add each item to the release checklist's Pending block with steps and the expected result, so a person checks it on a device.

A red result is information, not a verdict. Before calling a screen broken, seed it and look at it: a red smoke run is often a slow cold start, not a broken screen.

Setting up a new project

Copy in only what the project needs, in this order. Each template says at the top what it does and what to rename.

1. Component tests with React Native Testing Library, if not already there.
2. The test after edit hook: templates/ui-test-hook.sh into scripts/, and the hook block from templates/hook-settings.jsonc into .claude/settings.json. Edit the folder patterns at the top of the script.
3. The test seam: templates/e2eEnabled.ts, templates/testSeed.ts and the handler in templates/native-intent.ts. Replace <your-scheme> with the app's URL scheme and fill in the seeding for your own stores.
4. The smoke tier: templates/smoke/_screen.yaml, templates/smoke/manifest.mjs, and templates/check-e2e-coverage.mjs. Add the coverage check to the project's check command.
5. Journeys: start from templates/journey.yaml for the two or three paths that matter most (onboarding, the core action, the paywall).

Steps 4 and 5 use Maestro because that is what these templates were proven with. Expo has its own route for the same layer: e2e by TesterArmy, run locally and then on every pull request with EAS Workflows and Expo's hosted simulators (https://docs.expo.dev/guides/using-e2e/, read 2026-10-20). If the project already uses EAS Workflows, offer it as the option. The Last Mile has not run it on a real app yet, so say that.

A website instead of an app

The rule is the same; the tools are simpler, because the real screen is a browser and every environment, cloud sessions included, can run one.

• Behaviour: component tests with the project's runner (Vitest or Jest with Testing Library), written first and watched failing, exactly as in step 2.
• Look: run the site (the dev server, or the branch's preview deploy if the host makes one), open the page with Playwright and screenshot it at 390 by 844 and at 1280 by 800. Read both images. Most layout bugs on a website only show at one of the two widths.
• Signed in pages: sign in through the real form in the script, with a test account, never by pasting a session cookie into the code. Stub nothing you can run for real.
• Journeys: a Playwright test that starts at the URL a person actually arrives on (the home page, a shared link, a search result) and asserts the page it lands on and the words that matter there.
• Before calling it shipped: look at the live site once the deploy finishes. A preview that works can still break in production on environment values, caching or a different database.

Content capture for marketing video is a separate, experimental recipe: references/content-capture.md. Skip it unless the user asks.

Limits, stated plainly

• Component tests cannot see geometry. A test can pass while the text is hidden under a header.
• The smoke tier proves each screen mounts. It says nothing about layout.
• A seeded screen proves how the screen looks, not how a person reaches it.
• The browser preview is not a phone: no gestures, no native modules, no real safe areas or scroll geometry.
• Simulators need a Mac. Cameras, real purchases and push notifications need a real device.