eslint/docs/src/developer-guide/unit-tests.md

   1 ---
   2 title: Unit Tests
   3 layout: doc
   4 eleventyNavigation:
   5     key: run the tests
   6     parent: developer guide
   7     title: Run the Tests
   8     order: 3
   9
  10 ---
  11
  12 Most parts of ESLint have unit tests associated with them. Unit tests are written using [Mocha](https://mochajs.org/) and are required when making contributions to ESLint. You'll find all of the unit tests in the `tests` directory.
  13
  14 When you first get the source code, you need to run `npm install` once initially to set ESLint for development. Once you've done that, you can run the tests via:
  15
  16 ```shell
  17 npm test
  18 ```
  19
  20 This automatically starts Mocha and runs all tests in the `tests` directory. You need only add yours and it will automatically be picked up when running tests.
  21
  22 ## Running Individual Tests
  23
  24 If you want to quickly run just one test file, you can do so by running Mocha directly and passing in the filename. For example:
  25
  26 ```shell
  27 npm run test:cli tests/lib/rules/no-undef.js
  28 ```
  29
  30 If you want to run just one or a subset of `RuleTester` test cases, add `only: true` to each test case or wrap the test case in `RuleTester.only(...)` to add it automatically:
  31
  32 ```js
  33 ruleTester.run("my-rule", myRule, {
  34     valid: [
  35         RuleTester.only("const valid = 42;"),
  36         // Other valid cases
  37     ],
  38     invalid: [
  39         {
  40             code: "const invalid = 42;",
  41             only: true,
  42         },
  43         // Other invalid cases
  44     ]
  45 })
  46 ```
  47
  48 Running individual tests is useful when you're working on a specific bug and iterating on the solution. You should be sure to run `npm test` before submitting a pull request. `npm test` uses Mocha's `--forbid-only` option to prevent `only` tests from passing full test runs.
  49
  50 ## More Control on Unit Testing
  51
  52 `npm run test:cli` is an alias of the Mocha cli in `./node_modules/.bin/mocha`. [Options](https://mochajs.org/#command-line-usage) are available to be provided to help to better control the test to run.
  53
  54 The default timeout for tests in `npm test` is 10000ms. You may change the timeout by providing `ESLINT_MOCHA_TIMEOUT` environment variable, for example:
  55
  56 ```shell
  57 ESLINT_MOCHA_TIMEOUT=20000 npm test
  58 ```