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puppeteer/test/README.md
Jack Franklin 17cd8703f9
chore: migrate unit tests to Mocha (#5600) 
Rather than maintain our own test runner we should instead lean on the community and use Mocha which is very popular and also our test runner of choice in DevTools too.

Note that this commit doesn't remove the TestRunner source as it's still used for other unit tests, but they will be updated in a future PR and then we can remove the TestRunner.

The main bulk of this PR is updating the tests as the old TestRunner passed in contextual data via the `it` function callback whereas Mocha does not, so we introduce some helpers for the tests to make it easier.
2020-04-09 07:56:25 +02:00

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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 for Firefox

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 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.