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tests/wpt/web-platform-tests/docs/writing-tests/lint-tool.md

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+# Lint Tool
+
+We have a lint tool for catching common mistakes in test files. You can run
+it manually by running the `wpt lint` command from the root of your local
+web-platform-tests working directory like this:
+
+```
+./wpt lint
+```
+
+The lint tool is also run automatically for every submitted pull request,
+and reviewers will not merge branches with tests that have lint errors, so
+you must either [fix all lint errors](#fixing-lint-errors), or you must
+[whitelist test files](#updating-the-whitelist) to suppress the errors.
+
+## Fixing lint errors
+
+You must fix any errors the lint tool reports, unless an error is for
+something essential to a certain test or that for some other
+exceptional reason shouldn't prevent the test from being merged; in
+those cases you can [whitelist test files](#updating-the-whitelist)
+to suppress the errors. In all other cases, follow the instructions
+below to fix all errors reported.
+
+* **CONSOLE**: Test-file line has a `console.*(...)` call; **fix**: remove
+  the `console.*(...)` call (and in some cases, consider adding an
+  `assert_*` of some kind in place of it).
+
+* **CR AT EOL**: Test-file line ends with CR (U+000D) character; **fix**:
+  reformat file so each line just has LF (U+000A) line ending (standard,
+  cross-platform "Unix" line endings instead of, e.g., DOS line endings).
+
+* **EARLY-TESTHARNESSREPORT**: Test file has an instance of
+  `<script src='/resources/testharnessreport.js'>` prior to
+  `<script src='/resources/testharness.js'>`; **fix**: flip the order.
+
+* **GENERATE_TESTS**: Test file line has a generate_tests call; **fix**: remove
+  the call and call `test()` a number of times instead.
+
+* **INDENT TABS**: Test-file line starts with one or more tab characters;
+  **fix**: use spaces to replace any tab characters at beginning of lines.
+
+* **INVALID-TIMEOUT**: Test file with `<meta name='timeout'...>` element
+  that has a `content` attribute whose value is not `long`; **fix**:
+  replace the value of the `content` attribute with `long`.
+
+* **LATE-TIMEOUT**: Test file with `<meta name="timeout"...>` element after
+  `<script src='/resources/testharnessreport.js'>` element ; **fix**: move
+  the `<meta name="timeout"...>` element to precede the `script` element.
+
+* **LAYOUTTESTS APIS**: Test file uses `eventSender`, `testRunner`, or
+  `internals` which are LayoutTests-specific APIs used in WebKit/Blink.
+
+* **MALFORMED-VARIANT**: Test file with a `<meta name='variant'...>`
+  element whose `content` attribute has a malformed value; **fix**: ensure
+  the value of the `content` attribute starts with `?` or `#` or is empty.
+
+* **MISSING-LINK**: CSS test file is missing a link to a spec. **fix**: Ensure that there is a `<link rel="help" href="[url]">` for the spec.
+  * Note: `MISSING-LINK` is designed to ensure that the CSS build tool can find the tests. Note that the CSS build system is primarily used by [test.csswg.org/](http://test.csswg.org/), which doesn't use `wptserve`, so `*.any.js` and similar tests won't work there; stick with the `.html` equivalent.
+
+* **MISSING-TESTHARNESSREPORT**: Test file is missing an instance of
+  `<script src='/resources/testharnessreport.js'>`; **fix**: ensure each
+  test file contains `<script src='/resources/testharnessreport.js'>`.
+
+* **MULTIPLE-TESTHARNESS**: Test file with multiple instances of
+  `<script src='/resources/testharness.js'>`; **fix**: ensure each test
+  has only one `<script src='/resources/testharness.js'>` instance.
+
+* **MULTIPLE-TESTHARNESSREPORT**: Test file with multiple instances of
+  `<script src='/resources/testharnessreport.js'>`; **fix**: ensure each test
+  has only one `<script src='/resources/testharnessreport.js'>` instance.
+
+* **MULTIPLE-TIMEOUT**: Test file with multiple `<meta name="timeout"...>`
+  elements; **fix**: ensure each test file has only one instance of a
+  `<meta name="timeout"...>` element.
+
+* **PARSE-FAILED**: Test file failed parsing by manifest builder; **fix**:
+  examine the file to find the causes of any parse errors, and fix them.
+
+* **PATH LENGTH**: Test file's pathname has a total length greater than 150
+  characters; **fix**: use shorter filename to rename the test file.
+
+* **PRINT STATEMENT**: A server-side python support file contains a `print`
+  statement; **fix**: remove the `print` statement or replace it with
+  something else that achieves the intended effect (e.g., a logging call).
+
+* **SET TIMEOUT**: Test-file line has `setTimeout(...)` call; **fix**:
+  replace all `setTimeout(...)` calls with `step_timeout(...)` calls.
+
+* **TRAILING WHITESPACE**: Test-file line has trailing whitespace; **fix**:
+  remove trailing whitespace from all lines in the file.
+
+* **VARIANT-MISSING**: Test file with a `<meta name='variant'...>` element
+  that's missing a `content` attribute; **fix**: add a `content` attribute
+  with an appropriate value to the `<meta name='variant'...>` element.
+
+* **W3C-TEST.ORG**: Test-file line has the string `w3c-test.org`; **fix**:
+  either replace the `w3c-test.org` string with the expression
+  `{{host}}:{{ports[http][0]}}` or a generic hostname like `example.org`.
+
+## Updating the whitelist
+
+Normally you must [fix all lint errors](#fixing-lint-errors). But in the
+unusual case of error reports for things essential to certain tests or that
+for other exceptional reasons shouldn't prevent a merge of a test, you can
+update and commit the `lint.whitelist` file in the web-platform-tests root
+directory to suppress errors the lint tool would report for a test file.
+
+To add a test file or directory to the whitelist, use the following format:
+
+```
+ERROR TYPE:file/name/pattern
+```
+
+For example, to whitelist the file `example/file.html` such that all
+`TRAILING WHITESPACE` errors the lint tool would report for it are
+suppressed, add the following line to the `lint.whitelist` file:
+
+```
+TRAILING WHITESPACE:example/file.html
+```
+
+To whitelist an entire directory rather than just one file, use the `*`
+wildcard. For example, to whitelist the `example` directory such that all
+`TRAILING WHITESPACE` errors the lint tool would report for any files in it
+are suppressed, add the following line to the `lint.whitelist` file:
+
+```
+TRAILING WHITESPACE:example/*
+```
+
+Similarly, you can also
+use
+[shell-style wildcards](https://docs.python.org/2/library/fnmatch.html) to
+express other filename patterns or directory-name patterns.
+
+Finally, to whitelist just one line in a file, use the following format:
+
+```
+ERROR TYPE:file/name/pattern:line_number
+```
+
+For example, to whitelist just line 128 of the file `example/file.html`
+such that any `TRAILING WHITESPACE` error the lint tool would report for
+that line is suppressed, add the following to the `lint.whitelist` file:
+
+```
+TRAILING WHITESPACE:example/file.html:128
+```