Add support for testing the WebExtensions API in WPT #219
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| # RFC #219: Add support for WebExtensions in WPT | ||||||
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| ## Summary | ||||||
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| The WebExtensions API extends the capabilities of the browser. Adding support | ||||||
| for WebExtensions in the web platform tests will increase interoperability | ||||||
| and will help drive the standardization of this API. | ||||||
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| This RFC proposes adding a new `testharness.js` test type, `.extension.js`, to handle | ||||||
| testing this API, in addition to using `testdriver.js` to load and unload extensions. | ||||||
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| ## Details | ||||||
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| Using `testdriver.js`, we added support for testing the WebExtensions API by loading | ||||||
| a web extension designed to test the functionality of a specific API. | ||||||
| The extension will be loaded after the tests begins, and unloaded before the | ||||||
| test is finished. | ||||||
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There was a problem hiding this comment. We probably don't need this; technically people writing tests can do whatever, and I don't think we need to justify this. I'd probably add:
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| Most of the test execution is handled within the extension, via the | ||||||
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There was a problem hiding this comment. I think we need a sentence preceding this, maybe the one from the following paragraph?
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| [browser.test](https://chromium.googlesource.com/chromium/src.git/+/master/extensions/docs/testing_api.md) | ||||||
| API. We’ve elected to use these APIs since all participating browser vendors use | ||||||
| `browser.test` internally and they can easily port over existing tests to | ||||||
| the web platform tests. | ||||||
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| Because these tests won’t leverage `testharness.js` directly, we’ve introduced a new | ||||||
| `testharness.js`, `.extension.js`, that will create the necessary boilerplate to | ||||||
| convert the `browser.test` assertions into the corresponding assertions in the test | ||||||
| harness. | ||||||
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There was a problem hiding this comment. We should probably care to some extent about how easy/difficult it is to write tests without using Rather than putting all the code necessary to map from |
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| A proposed patch is available at https://github.com/web-platform-tests/wpt/pull/50648. | ||||||
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| ## Alternatives considered | ||||||
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| We considered loading the extension statically before each `testharness.js` test is run, | ||||||
| but we decided against that since `testdriver.js` will allow the tests to drive the | ||||||
| browser, and in the future, test functionality such as opening popups and clicking | ||||||
| menu items. | ||||||
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| We considered adding a new test type rather than using JavaScript tests, but we decided | ||||||
| against it because it was a lot more work compared to using `testharness.js`. | ||||||
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| ## Risks | ||||||
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| There are two potential concerns with this implementation: | ||||||
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| 1. We have no precedent for tests run via a Classic command in some user agents | ||||||
| and BiDi command in others. However, the Classic implementation of loading | ||||||
| and unloading extension is modeled on the BiDi implementation, so we expect the | ||||||
| behavior to be the same. The Classic implementation is defined in the WebExtensions Community Group | ||||||
| [here](https://github.com/w3c/webextensions/blob/main/specification/webdriver-classic.bs), | ||||||
| and the BiDi implementation is defined | ||||||
| [here](https://www.w3.org/TR/webdriver-bidi/#module-webExtension). | ||||||
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| 2. Another concern could be with using `browser.test` assertions and mapping them to | ||||||
| `testharness.js` assertions. With `testharness.js` not in charge of generating assertions, | ||||||
| we might end up with less useful failure messages. | ||||||
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This technically isn't a new test type (because the manifest will still make it a testharness test), it's just server-side support for creating them from a pure JS file.
We could potentially split this out into a separate RFC, but that's probably only worthwhile if we start having significant debates about whether/what that support should be.