test

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test provides a standard way of writing and running tests in Dart.

Writing Tests

Tests are specified using the top-level test() function, and test assertions are made using expect():

import "package:test/test.dart";

void main() {
  test("String.split() splits the string on the delimiter", () {
    var string = "foo,bar,baz";
    expect(string.split(","), equals(["foo", "bar", "baz"]));
  });

  test("String.trim() removes surrounding whitespace", () {
    var string = "  foo ";
    expect(string.trim(), equals("foo"));
  });
}

Tests can be grouped together using the [group()] function. Each group's description is added to the beginning of its test's descriptions.

import "package:test/test.dart";

void main() {
  group("String", () {
    test(".split() splits the string on the delimiter", () {
      var string = "foo,bar,baz";
      expect(string.split(","), equals(["foo", "bar", "baz"]));
    });

    test(".trim() removes surrounding whitespace", () {
      var string = "  foo ";
      expect(string.trim(), equals("foo"));
    });
  });

  group("int", () {
    test(".remainder() returns the remainder of division", () {
      expect(11.remainder(3), equals(2));
    });

    test(".toRadixString() returns a hex string", () {
      expect(11.toRadixString(16), equals("b"));
    });
  });
}

Any matchers from the matcher package can be used with expect() to do complex validations:

import "package:test/test.dart";

void main() {
  test(".split() splits the string on the delimiter", () {
    expect("foo,bar,baz", allOf([
      contains("foo"),
      isNot(startsWith("bar")),
      endsWith("baz")
    ]));
  });
}

Running Tests

A single test file can be run just using pub run test:test path/to/test.dart (on Dart 1.10, this can be shortened to pub run test path/to/test.dart).

Single file being run via pub run"

Many tests can be run at a time using pub run test:test path/to/dir.

Directory being run via "pub run".

It's also possible to run a test on the Dart VM only by invoking it using dart path/to/test.dart, but this doesn't load the full test runner and will be missing some features.

The test runner considers any file that ends with _test.dart to be a test file. If you don't pass any paths, it will run all the test files in your test/ directory, making it easy to test your entire application at once.

By default, tests are run in the Dart VM, but you can run them in the browser as well by passing pub run test:test -p chrome path/to/test.dart. test will take care of starting the browser and loading the tests, and all the results will be reported on the command line just like for VM tests. In fact, you can even run tests on both platforms with a single command: pub run test:test -p chrome,vm path/to/test.dart.

Restricting Tests to Certain Platforms

Some test files only make sense to run on particular platforms. They may use dart:html or dart:io, they might test Windows' particular filesystem behavior, or they might use a feature that's only available in Chrome. The @TestOn annotation makes it easy to declare exactly which platforms a test file should run on. Just put it at the top of your file, before any library or import declarations:

@TestOn("vm")

import "dart:io";

import "package:test/test.dart";

void main() {
  // ...
}

The string you pass to @TestOn is what's called a "platform selector", and it specifies exactly which platforms a test can run on. It can be as simple as the name of a platform, or a more complex Dart-like boolean expression involving these platform names.

Platform Selector Syntax

Platform selectors can contain identifiers, parentheses, and operators. When loading a test, each identifier is set to true or false based on the current platform, and the test is only loaded if the platform selector returns true. The operators ||, &&, !, and ? : all work just like they do in Dart. The valid identifiers are:

• vm: Whether the test is running on the command-line Dart VM.

• dartium: Whether the test is running on Dartium.

• content-shell: Whether the test is running on the headless Dartium content shell.

• chrome: Whether the test is running on Google Chrome.

• phantomjs: Whether the test is running on PhantomJS.

• firefox: Whether the test is running on Mozilla Firefox.

• safari: Whether the test is running on Apple Safari.

• ie: Whether the test is running on Microsoft Internet Explorer.

• dart-vm: Whether the test is running on the Dart VM in any context, including Dartium. It's identical to !js.

• browser: Whether the test is running in any browser.

• js: Whether the test has been compiled to JS. This is identical to !dart-vm.

• blink: Whether the test is running in a browser that uses the Blink rendering engine.

• windows: Whether the test is running on Windows. If vm is false, this will be false as well.

• mac-os: Whether the test is running on Mac OS. If vm is false, this will be false as well.

• linux: Whether the test is running on Linux. If vm is false, this will be false as well.

• android: Whether the test is running on Android. If vm is false, this will be false as well, which means that this won't be true if the test is running on an Android browser.

• posix: Whether the test is running on a POSIX operating system. This is equivalent to !windows.

For example, if you wanted to run a test on every browser but Chrome, you would write @TestOn("browser && !chrome").

Running Tests on Dartium

Tests can be run on Dartium by passing the -p dartium flag. If you're using the Dart Editor, the test runner will be able to find Dartium automatically. On Mac OS, you can also install it using Homebrew. Otherwise, make sure there's an executable called dartium (on Mac OS or Linux) or dartium.exe (on Windows) on your system path.

Similarly, tests can be run on the headless Dartium content shell by passing -p content-shell. The content shell is installed along with Dartium when using Homebrew. Otherwise, you can downloaded it manually from this page; if you do, make sure the executable named content_shell (on Mac OS or Linux) or content_shell.exe (on Windows) is on your system path.

In the future, there will be a more explicit way to configure the location of both the Dartium and content shell executables.

Asynchronous Tests

Tests written with async/await will work automatically. The test runner won't consider the test finished until the returned Future completes.

import "dart:async";

import "package:test/test.dart";

void main() {
  test("new Future.value() returns the value", () async {
    var value = await new Future.value(10);
    expect(value, equals(10));
  });
}

There are also a number of useful functions and matchers for more advanced asynchrony. The completion() matcher can be used to test Futures; it ensures that the test doesn't finish until the Future completes, and runs a matcher against that Future's value.

import "dart:async";

import "package:test/test.dart";

void main() {
  test("new Future.value() returns the value", () {
    expect(new Future.value(10), completion(equals(10)));
  });
}

The [throwsA()][throwsA] matcher and the various throwsExceptionType matchers work with both synchronous callbacks and asynchronous Futures. They ensure that a particular type of exception is thrown:

import "dart:async";

import "package:test/test.dart";

void main() {
  test("new Future.error() throws the error", () {
    expect(new Future.error("oh no"), throwsA(equals("oh no")));
    expect(new Future.error(new StateError("bad state")), throwsStateError);
  });
}

The expectAsync() function wraps another function and has two jobs. First, it asserts that the wrapped function is called a certain number of times, and will cause the test to fail if it's called too often; second, it keeps the test from finishing until the function is called the requisite number of times.

import "dart:async";

import "package:test/test.dart";

void main() {
  test("Stream.fromIterable() emits the values in the iterable", () {
    var stream = new Stream.fromIterable([1, 2, 3]);

    stream.listen(expectAsync((number) {
      expect(number, inInclusiveRange(1, 3));
    }, count: 3));
  });
}

Running Tests with Custom HTML

By default, the test runner will generate its own empty HTML file for browser tests. However, tests that need custom HTML can create their own files. These files have three requirements:

• They must have the same name as the test, with .dart replaced by .html.

• They must contain a link tag with rel="x-dart-test" and an href attribute pointing to the test script.

• They must contain <script src="packages/test/dart.js"></script>.

For example, if you had a test called custom_html_test.dart, you might write the following HTML file:

<!doctype html>
<!-- custom_html_test.html -->
<html>
  <head>
    <title>Custom HTML Test</title>
    <link rel="x-dart-test" href="custom_html_test.dart">
    <script src="packages/test/dart.js"></script>
  </head>
  <body>
    // ...
  </body>
</html>

Configuring Tests

Skipping Tests

If a test, group, or entire suite isn't working yet and you just want it to stop complaining, you can mark it as "skipped". The test or tests won't be run, and, if you supply a reason why, that reason will be printed. In general, skipping tests indicates that they should run but is temporarily not working. If they're is fundamentally incompatible with a platform, @TestOn/testOn should be used instead.

To skip a test suite, put a @Skip annotation at the top of the file:

@Skip("currently failing (see issue 1234)")

import "package:test/test.dart";

void main() {
  // ...
}

The string you pass should describe why the test is skipped. You don't have to include it, but it's a good idea to document why the test isn't running.

Groups and individual tests can be skipped by passing the skip parameter. This can be either true or a String describing why the test is skipped. For example:

import "package:test/test.dart";

void main() {
  group("complicated algorithm tests", () {
    // ...
  }, skip: "the algorithm isn't quite right");

  test("error-checking test", () {
    // ...
  }, skip: "TODO: add error-checking.");
}

Timeouts

By default, tests will time out after 30 seconds of inactivity. However, this can be configured on a per-test, -group, or -suite basis. To change the timeout for a test suite, put a @Timeout annotation at the top of the file:

@Timeout(const Duration(seconds: 45))

import "package:test/test.dart";

void main() {
  // ...
}

In addition to setting an absolute timeout, you can set the timeout relative to the default using @Timeout.factor. For example, @Timeout.factor(1.5) will set the timeout to one and a half times as long as the default—45 seconds.

Timeouts can be set for tests and groups using the timeout parameter. This parameter takes a Timeout object just like the annotation. For example:

import "package:test/test.dart";

void main() {
  group("slow tests", () {
    // ...

    test("even slower test", () {
      // ...
    }, timeout: new Timeout.factor(2))
  }, timeout: new Timeout(new Duration(minutes: 1)));
}

Nested timeouts apply in order from outermost to innermost. That means that "even slower test" will take two minutes to time out, since it multiplies the group's timeout by 2.

Platform-Specific Configuration

Sometimes a test may need to be configured differently for different platforms. Windows might run your code slower than other platforms, or your DOM manipulation might not work right on Safari yet. For these cases, you can use the @OnPlatform annotation and the onPlatform named parameter to test() and group(). For example:

@OnPlatform(const {
  // Give Windows some extra wiggle-room before timing out.
  "windows": const Timeout.factor(2)
})

import "package:test/test.dart";

void main() {
  test("do a thing", () {
    // ...
  }, onPlatform: {
    "safari": new Skip("Safari is currently broken (see #1234)")
  });
}

Both the annotation and the parameter take a map. The map's keys are platform selectors which describe the platforms for which the specialized configuration applies. Its values are instances of some of the same annotation classes that can be used for a suite: Skip and Timeout. A value can also be a list of these values.

If multiple platforms match, the configuration is applied in order from first to last, just as they would in nested groups. This means that for configuration like duration-based timeouts, the last matching value wins.

Testing With barback

Packages using the barback transformer system may need to test code that's created or modified using transformers. The test runner handles this using the --pub-serve option, which tells it to load the test code from a pub serve instance rather than from the filesystem. This feature is only supported on Dart 1.9.2 and higher.

Before using the --pub-serve option, add the test/pub_serve transformer to your pubspec.yaml. This transformer adds the necessary bootstrapping code that allows the test runner to load your tests properly:

transformers:
- test/pub_serve:
    $include: test/**_test{.*,}.dart

Note that if you're using the test runner along with polymer, you have to make sure that the test/pub_serve transformer comes after the polymer transformer:

transformer:
- polymer
- test/pub_serve:
    $include: test/**_test{.*,}.dart

Then, start up pub serve. Make sure to pay attention to which port it's using to serve your test/ directory:

$ pub serve
Loading source assets...
Loading test/pub_serve transformers...
Serving my_app web on http://localhost:8080
Serving my_app test on http://localhost:8081
Build completed successfully

In this case, the port is 8081. In another terminal, pass this port to --pub-serve and otherwise invoke pub run test:test as normal:

$ pub run test:test --pub-serve=8081 -p chrome
"pub serve" is compiling test/my_app_test.dart...
"pub serve" is compiling test/utils_test.dart...
00:00 +42: All tests passed!