# Mix v1.10.3 mix test View Source

Runs the tests for a project.

This task starts the current application, loads up `test/test_helper.exs` and then requires all files matching the `test/**/*_test.exs` pattern in parallel.

A list of files can be given after the task name in order to select the files to compile:

    mix test test/some/particular/file_test.exs

Tests in umbrella projects can be run from the root by specifying the full suite path, including `apps/my_app/test`, in which case recursive tests for other child apps will be skipped completely:

    # To run all tests for my_app from the umbrella root
    mix test apps/my_app/test

    # To run a given test file on my_app from the umbrella root
    mix test apps/my_app/test/some/particular/file_test.exs

## Command line options

- `--color` - enables color in the output
- `--cover` - runs coverage tool. See "Coverage" section below
- `--exclude` - excludes tests that match the filter
- `--failed` - runs only tests that failed the last time they ran
- `--force` - forces compilation regardless of modification times
- `--formatter` - sets the formatter module that will print the results. Defaults to ExUnit's built-in CLI formatter
- `--include` - includes tests that match the filter
- `--listen-on-stdin` - runs tests, and then listens on stdin. Receiving a newline will result in the tests being run again. Very useful when combined with `--stale` and external commands which produce output on stdout upon file system modifications
- `--max-cases` - sets the maximum number of tests running asynchronously. Only tests from different modules run in parallel. Defaults to twice the number of cores
- `--max-failures` - the suite stops evaluating tests when this number of test failures is reached. It runs all tests if omitted
- `--no-archives-check` - does not check archives
- `--no-color` - disables color in the output
- `--no-compile` - does not compile, even if files require compilation
- `--no-deps-check` - does not check dependencies
- `--no-elixir-version-check` - does not check the Elixir version from `mix.exs`
- `--no-start` - does not start applications after compilation
- `--only` - runs only tests that match the filter
- `--partitions` - sets the amount of partitions to split tests in. This option requires the `MIX_TEST_PARTITION` environment variable to be set. See the "Operating system process partitioning" section for more information
- `--preload-modules` - preloads all modules defined in applications
- `--raise` - raises if the test suite failed
- `--seed` - seeds the random number generator used to randomize the order of tests; `--seed 0` disables randomization
- `--slowest` - prints timing information for the N slowest tests. Automatically sets `--trace` and `--preload-modules`
- `--stale` - runs only tests which reference modules that changed since the last time tests were ran with `--stale`. You can read more about this option in the "The --stale option" section below
- `--timeout` - sets the timeout for the tests
- `--trace` - runs tests with detailed reporting. Automatically sets `--max-cases` to `1`. Note that in trace mode test timeouts will be ignored as timeout is set to `:infinity`

## Configuration

These configurations can be set in the `def project` section of your `mix.exs`:

- `:test_paths` - list of paths containing test files. Defaults to `["test"]` if the `test` directory exists; otherwise, it defaults to `[]`. It is expected that all test paths contain a `test_helper.exs` file

- `:test_pattern` - a pattern to load test files. Defaults to `*_test.exs`

- `:warn_test_pattern` - a pattern to match potentially misnamed test files and display a warning. Defaults to `*_test.ex`

- `:test_coverage` - a set of options to be passed down to the coverage mechanism

## Filters

ExUnit provides tags and filtering functionality that allow developers to select which tests to run. The most common functionality is to exclude some particular tests from running by default in your test helper file:

    # Exclude all external tests from running
    ExUnit.configure(exclude: [external: true])

Then, whenever desired, those tests could be included in the run via the `--include` option:

    mix test --include external:true

The example above will run all tests that have the external option set to `true`. It is also possible to include all examples that have a given tag, regardless of its value:

    mix test --include external

Note that all tests are included by default, so unless they are excluded first (either in the test helper or via the `--exclude` option) the `--include` option has no effect.

For this reason, Mix also provides an `--only` option that excludes all tests and includes only the given ones:

    mix test --only external

Which is similar to:

    mix test --include external --exclude test

It differs in that the test suite will fail if no tests are executed when the `--only` option is used.

In case a single file is being tested, it is possible to pass one or more specific line numbers to run only those given tests:

    mix test test/some/particular/file_test.exs:12

Which is equivalent to:

    mix test --exclude test --include line:12 test/some/particular/file_test.exs

Or:

    mix test test/some/particular/file_test.exs:12:24

Which is equivalent to:

    mix test --exclude test --include line:12 --include line:24 test/some/particular/file_test.exs

If a given line starts a `describe` block, that line filter runs all tests in it. Otherwise, it runs the closest test on or before the given line number.

## Coverage

The `:test_coverage` configuration accepts the following options:

- `:output` - the output directory for cover results. Defaults to `"cover"`
- `:tool` - the coverage tool
- `:summary` - summary output configuration; can be either a boolean or a keyword list. When a keyword list is passed, it can specify a `:threshold`, which is a boolean or numeric value that enables coloring of code coverage results in red or green depending on whether the percentage is below or above the specified threshold, respectively. Defaults to `[threshold: 90]`

By default, a very simple wrapper around OTP's `cover` is used as a tool, but it can be overridden as follows:

    def project() do
      [
        ...
        test_coverage: [tool: CoverModule]
        ...
      ]
    end

`CoverModule` can be any module that exports `start/2`, receiving the compilation path and the `test_coverage` options as arguments. It must return either `nil` or an anonymous function of zero arity that will be run after the test suite is done.

## Operating system process partitioning

While ExUnit supports the ability to run tests concurrently within the same Elixir instance, it is not always possible to run all tests concurrently. For example, some tests may rely on global resources.

For this reason, `mix test` supports partitioning the test files across different Elixir instances. This is done by setting the `--partitions` option to an integer, with the number of partitions, and setting the `MIX_TEST_PARTITION` environment variable to control which test partition that particular instance is running. This can also be useful if you want to distribute testing across multiple machines.

For example, to split a test suite into 4 partitions and run them, you would use the following commands:

    MIX_TEST_PARTITION=1 mix test --partitions 4
    MIX_TEST_PARTITION=2 mix test --partitions 4
    MIX_TEST_PARTITION=3 mix test --partitions 4
    MIX_TEST_PARTITION=4 mix test --partitions 4

The test files are sorted and distributed in a round-robin fashion. Note the partition itself is given as an environment variable so it can be accessed in configuration files and test scripts. For example, it can be used to setup a different database instance per partition in `config/test.exs`.

## The --stale option

The `--stale` command line option attempts to run only the test files which reference modules that have changed since the last time you ran this task with `--stale`.

The first time this task is run with `--stale`, all tests are run and a manifest is generated. On subsequent runs, a test file is marked "stale" if any modules it references (and any modules those modules reference, recursively) were modified since the last run with `--stale`. A test file is also marked "stale" if it has been changed since the last run with `--stale`.

The `--stale` option is extremely useful for software iteration, allowing you to run only the relevant tests as you perform changes to the codebase.