# `tornado.testing` — Unit testing support for asynchronous code

Support classes for automated testing.

- `AsyncTestCase` and `AsyncHTTPTestCase`: Subclasses of unittest.TestCase with additional support for testing asynchronous (`IOLoop`-based) code.

- `ExpectLog`: Make test logs less spammy.

- `main()`: A simple test runner (wrapper around unittest.main()) with support for the tornado.autoreload module to rerun the tests when code changes.

## Asynchronous test cases

class tornado.testing.AsyncTestCase(methodName: str = 'runTest')

  `TestCase` subclass for testing `IOLoop`-based asynchronous code.

  The unittest framework is synchronous, so the test must be complete by the time the test method returns. This means that asynchronous code cannot be used in quite the same way as usual and must be adapted to fit. To write your tests with coroutines, decorate your test methods with `tornado.testing.gen_test` instead of `tornado.gen.coroutine`.

  This class also provides the (deprecated) `stop()` and `wait()` methods for a more manual style of testing. The test method itself must call `self.wait()`, and asynchronous callbacks should call `self.stop()` to signal completion.

  By default, a new `IOLoop` is constructed for each test and is available as `self.io_loop`. If the code being tested requires a global `IOLoop`, subclasses should override `get_new_ioloop` to return it.

  The `IOLoop`’s `start` and `stop` methods should not be called directly. Instead, use `self.stop` and `self.wait`. Arguments passed to `self.stop` are returned from `self.wait`. It is possible to have multiple `wait`/`stop` cycles in the same test.

  Example:

      # This test uses coroutine style.
      class MyTestCase(AsyncTestCase):
          @tornado.testing.gen_test
          def test_http_fetch(self):
              client = AsyncHTTPClient()
              response = yield client.fetch("http://www.tornadoweb.org")
              # Test contents of response
              self.assertIn("FriendFeed", response.body)

      # This test uses argument passing between self.stop and self.wait.
      class MyTestCase2(AsyncTestCase):
          def test_http_fetch(self):
              client = AsyncHTTPClient()
              client.fetch("http://www.tornadoweb.org/", self.stop)
              response = self.wait()
              # Test contents of response
              self.assertIn("FriendFeed", response.body)

  get_new_ioloop() → tornado.ioloop.IOLoop

    Returns the `IOLoop` to use for this test.

    By default, a new `IOLoop` is created for each test. Subclasses may override this method to return `IOLoop.current()` if it is not appropriate to use a new `IOLoop` in each tests (for example, if there are global singletons using the default `IOLoop`) or if a per-test event loop is being provided by another system (such as `pytest-asyncio`).

  stop(_arg: Optional[Any] = None, **kwargs: Any) → None

    Stops the `IOLoop`, causing one pending (or future) call to `wait()` to return.

    Keyword arguments or a single positional argument passed to `stop()` are saved and will be returned by `wait()`.

    Deprecated since version 5.1: `stop` and `wait` are deprecated; use `@gen_test` instead.

  wait(condition: Optional[Callable[[...], bool]] = None, timeout: Optional[float] = None) → Any

    Runs the `IOLoop` until stop is called or timeout has passed.

    In the event of a timeout, an exception will be thrown. The default timeout is 5 seconds; it may be overridden with a `timeout` keyword argument or globally with the `ASYNC_TEST_TIMEOUT` environment variable.

    If `condition` is not `None`, the `IOLoop` will be restarted after `stop()` until `condition()` returns `True`.

    Changed in version 3.1: Added the `ASYNC_TEST_TIMEOUT` environment variable.

    Deprecated since version 5.1: `stop` and `wait` are deprecated; use `@gen_test` instead.

class tornado.testing.AsyncHTTPTestCase(methodName: str = 'runTest')

  A test case that starts up an HTTP server.

  Subclasses must override `get_app()`, which returns the `tornado.web.Application` (or other `HTTPServer` callback) to be tested. Tests will typically use the provided `self.http_client` to fetch URLs from this server.

  Example, assuming the “Hello, world” example from the user guide is in `hello.py`:

      import hello

      class TestHelloApp(AsyncHTTPTestCase):
          def get_app(self):
              return hello.make_app()

          def test_homepage(self):
              response = self.fetch('/')
              self.assertEqual(response.code, 200)
              self.assertEqual(response.body, 'Hello, world')

  That call to `self.fetch()` is equivalent to

      self.http_client.fetch(self.get_url('/'), self.stop)
      response = self.wait()

  which illustrates how AsyncTestCase can turn an asynchronous operation, like `http_client.fetch()`, into a synchronous operation. If you need to do other asynchronous operations in tests, you’ll probably need to use `stop()` and `wait()` yourself.

  get_app() → tornado.web.Application

    Should be overridden by subclasses to return a `tornado.web.Application` or other `HTTPServer` callback.

  fetch(path: str, raise_error: bool = False, **kwargs: Any) → tornado.httpclient.HTTPResponse

    Convenience method to synchronously fetch a URL.

    The given path will be appended to the local server’s host and port. Any additional keyword arguments will be passed directly to `AsyncHTTPClient.fetch` (and so could be used to pass `method="POST"`, `body="..."`, etc).

    If the path begins with http:// or https://, it will be treated as a full URL and will be fetched as-is.

    If `raise_error` is `True`, a `tornado.httpclient.HTTPError` will be raised if the response code is not 200. This is the same behavior as the `raise_error` argument to `AsyncHTTPClient.fetch`, but the default is `False` here (it’s `True` in `AsyncHTTPClient`) because tests often need to deal with non-200 response codes.

    Changed in version 5.0: Added support for absolute URLs.

    Changed in version 5.1: Added the `raise_error` argument.

    Deprecated since version 5.1: This method currently turns any exception into an `HTTPResponse` with status code 599. In Tornado 6.0, errors other than `tornado.httpclient.HTTPError` will be passed through, and `raise_error=False` will only suppress errors that would be raised due to non-200 response codes.

  get_httpserver_options() → Dict[str, Any]

    May be overridden by subclasses to return additional keyword arguments for the server.

  get_http_port() → int

    Returns the port used by the server.

    A new port is chosen for each test.

  get_url(path: str) → str

    Returns an absolute url for the given path on the test server.

class tornado.testing.AsyncHTTPSTestCase(methodName: str = 'runTest')

  A test case that starts an HTTPS server.

  Interface is generally the same as `AsyncHTTPTestCase`.

  get_ssl_options() → Dict[str, Any]

    May be overridden by subclasses to select SSL options.

    By default includes a self-signed testing certificate.

tornado.testing.gen_test(*, timeout: Optional[float] = 'None') → Callable[[Callable[..., Union[Generator, 'Coroutine']]], Callable[..., None]]
tornado.testing.gen_test(func: Callable[..., Union[Generator, 'Coroutine']]) → Callable[[...], None]

  Testing equivalent of `@gen.coroutine`, to be applied to test methods.

  `@gen.coroutine` cannot be used on tests because the `IOLoop` is not already running. `@gen_test` should be applied to test methods on subclasses of `AsyncTestCase`.

  Example:

      class MyTest(AsyncHTTPTestCase):
          @gen_test
          def test_something(self):
              response = yield self.http_client.fetch(self.get_url('/'))

  By default, `@gen_test` times out after 5 seconds. The timeout may be overridden globally with the `ASYNC_TEST_TIMEOUT` environment variable, or for each test with the `timeout` keyword argument:

      class MyTest(AsyncHTTPTestCase):
          @gen_test(timeout=10)
          def test_something_slow(self):
              response = yield self.http_client.fetch(self.get_url('/'))

  Note that `@gen_test` is incompatible with `AsyncTestCase.stop`, `AsyncTestCase.wait`, and `AsyncHTTPTestCase.fetch`. Use `yield self.http_client.fetch(self.get_url())` as shown above instead.

  New in version 3.1: The `timeout` argument and `ASYNC_TEST_TIMEOUT` environment variable.

  Changed in version 4.0: The wrapper now passes along `*args, **kwargs` so it can be used on functions with arguments.

## Controlling log output

class tornado.testing.ExpectLog(logger: Union[logging.Logger, str], regex: str, required: bool = True, level: Optional[int] = None)

  Context manager to capture and suppress expected log output.

  Useful to make tests of error conditions less noisy, while still leaving unexpected log entries visible. Not thread safe.

  The attribute `logged_stack` is set to `True` if any exception stack trace was logged.

  Usage:

      with ExpectLog('tornado.application', "Uncaught exception"):
          error_response = self.fetch("/some_page")

  Changed in version 4.3: Added the `logged_stack` attribute.

  Constructs an ExpectLog context manager.

  Parameters

    - logger – Logger object (or name of logger) to watch. Pass an empty string to watch the root logger.

    - regex – Regular expression to match. Any log entries on the specified logger that match this regex will be suppressed.

    - required – If true, an exception will be raised if the end of the `with` statement is reached without matching any log entries.

    - level – A constant from the `logging` module indicating the expected log level. If this parameter is provided, only log messages at this level will be considered to match. Additionally, the supplied `logger` will have its level adjusted if necessary (for the duration of the `ExpectLog` to enable the expected message.

  Changed in version 6.1: Added the `level` parameter.

## Test runner

tornado.testing.main(**kwargs: Any) → None

  A simple test runner.

  This test runner is essentially equivalent to `unittest.main` from the standard library, but adds support for Tornado-style option parsing and log formatting. It is not necessary to use this `main` function to run tests using `AsyncTestCase`; these tests are self-contained and can run with any test runner.

  The easiest way to run a test is via the command line:

      python -m tornado.testing tornado.test.web_test

  See the standard library `unittest` module for ways in which tests can be specified.

  Projects with many tests may wish to define a test script like `tornado/test/runtests.py`. This script should define a method `all()` which returns a test suite and then call `tornado.testing.main()`. Note that even when a test script is used, the `all()` test suite may be overridden by naming a single test on the command line:

      # Runs all tests
      python -m tornado.test.runtests
      # Runs one test
      python -m tornado.test.runtests tornado.test.web_test

  Additional keyword arguments passed through to `unittest.main()`. For example, use `tornado.testing.main(verbosity=2)` to show many test details as they are run. See http://docs.python.org/library/unittest.html#unittest.main for full argument list.

  Changed in version 5.0: This function produces no output of its own; only that produced by the `unittest` module (previously it would add a PASS or FAIL log message).

## Helper functions

tornado.testing.bind_unused_port(reuse_port: bool = False) → Tuple[socket.socket, int]

  Binds a server socket to an available port on localhost.

  Returns a tuple (socket, port).

  Changed in version 4.4: Always binds to `127.0.0.1` without resolving the name `localhost`.

tornado.testing.get_async_test_timeout() → float

  Get the global timeout setting for async tests.

  Returns a float, the timeout in seconds.

  New in version 3.1.