# Puppeteer unit tests

Unit tests in Puppeteer are written using [Mocha] as the test runner and [Expect] as the assertions library.

## Test state

We have some common setup that runs before each test and is defined in `mocha-utils.js`.

You can use the `getTestState` function to read state. It exposes the following that you can use in your tests. These will be reset/tidied between tests automatically for you:

- `puppeteer`: an instance of the Puppeteer library. This is exactly what you'd get if you ran `require('puppeteer')`.
- `puppeteerPath`: the path to the root source file for Puppeteer.
- `defaultBrowserOptions`: the default options the Puppeteer browser is launched from in test mode, so tests can use them and override if required.
- `server`: a dummy test server instance (see `utils/testserver` for more).
- `httpsServer`: a dummy test server HTTPS instance (see `utils/testserver` for more).
- `isFirefox`: true if running in Firefox.
- `isChrome`: true if running Chromium.
- `isHeadless`: true if the test is in headless mode.

If your test needs a browser instance, you can use the `setupTestBrowserHooks()` function which will automatically configure a browser that will be cleaned between each test suite run. You access this via `getTestState()`.

If your test needs a Puppeteer page and context, you can use the `setupTestPageAndContextHooks()` function which will configure these. You can access `page` and `context` from `getTestState()` once you have done this.

The best place to look is an existing test to see how they use the helpers.

## Skipping tests in specific conditions

Tests that are not expected to pass in Firefox can be skipped. You can skip an individual test by using `itFailsFirefox` rather than `it`. Similarly you can skip a describe block with `describeFailsFirefox`.

There is also `describeChromeOnly` and `itChromeOnly` which will only execute the test if running in Chromium. Note that this is different from `describeFailsFirefox`: the goal is to get any `FailsFirefox` calls passing in Firefox, whereas `describeChromeOnly` should be used to test behaviour that will only ever apply in Chromium.

There are also tests that assume a normal install flow, with browser binaries ending up in `.local-<browser>`, for example. Such tests are skipped with
`itOnlyRegularInstall` which checks `BINARY` and `PUPPETEER_ALT_INSTALL` environment variables.

[mocha]: https://mochajs.org/
[expect]: https://www.npmjs.com/package/expect

## Running tests

Despite being named 'unit', these are integration tests, making sure public API methods and events work as expected.

- To run all tests:

```bash
npm run unit
```

- **Important**: don't forget to first run TypeScript if you're testing local changes:

```bash
npm run tsc && npm run unit
```

- To run a specific test, substitute the `it` with `it.only`:

```js
  ...
  it.only('should work', async function() {
    const {server, page} = getTestState();
    const response = await page.goto(server.EMPTY_PAGE);
    expect(response.ok).toBe(true);
  });
```

- To disable a specific test, substitute the `it` with `xit` (mnemonic rule: '_cross it_'):

```js
  ...
  // Using "xit" to skip specific test
  xit('should work', async function({server, page}) {
    const {server, page} = getTestState();
    const response = await page.goto(server.EMPTY_PAGE);
    expect(response.ok).toBe(true);
  });
```

- To run tests in non-headless mode:

```bash
HEADLESS=false npm run unit
```

- To run tests with custom browser executable:

```bash
BINARY=<path-to-executable> npm run unit
```