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class

test.TestContext

class TestContext

An instance of TestContext is passed to each test function in order to interact with the test runner. However, the TestContext constructor is not exposed as part of the API.

  • readonly assert: TestContextAssert

    An object containing assertion methods bound to the test context. The top-level functions from the node:assert module are exposed here for the purpose of creating test plans.

    Note: Some of the functions from node:assert contain type assertions. If these are called via the TestContext assert object, then the context parameter in the test's function signature must be explicitly typed (ie. the parameter must have a type annotation), otherwise an error will be raised by the TypeScript compiler:

    import { test, type TestContext } from 'node:test';

// The test function's context parameter must have a type annotation.
test('example', (t: TestContext) => {
  t.assert.deepStrictEqual(actual, expected);
});

// Omitting the type annotation will result in a compilation error.
test('example', t => {
  t.assert.deepStrictEqual(actual, expected); // Error: 't' needs an explicit type annotation.
});
  • readonly filePath: undefined | string

    The absolute path of the test file that created the current test. If a test file imports additional modules that generate tests, the imported tests will return the path of the root test file.

  • readonly fullName: string

    The name of the test and each of its ancestors, separated by >.

  • readonly mock: MockTracker

    Each test provides its own MockTracker instance.

  • readonly name: string

    The name of the test.

  • readonly signal: AbortSignal
    test('top level test', async (t) => {
  await fetch('some/uri', { signal: t.signal });
});
  • test: typeof test

    This function is used to create subtests under the current test. This function behaves in the same fashion as the top level test function.

  • fn?: TestContextHookFn,
    options?: HookOptions
    ): void;

    This function is used to create a hook that runs after the current test finishes.

    @param fn

    The hook function. The first argument to this function is a TestContext object. If the hook uses callbacks, the callback function is passed as the second argument.

    @param options

    Configuration options for the hook.

  • fn?: TestContextHookFn,
    options?: HookOptions
    ): void;

    This function is used to create a hook running after each subtest of the current test.

    @param fn

    The hook function. The first argument to this function is a TestContext object. If the hook uses callbacks, the callback function is passed as the second argument.

    @param options

    Configuration options for the hook.

  • fn?: TestContextHookFn,
    options?: HookOptions
    ): void;

    This function is used to create a hook running before subtest of the current test.

    @param fn

    The hook function. The first argument to this function is a TestContext object. If the hook uses callbacks, the callback function is passed as the second argument.

    @param options

    Configuration options for the hook.

  • fn?: TestContextHookFn,
    options?: HookOptions
    ): void;

    This function is used to create a hook running before each subtest of the current test.

    @param fn

    The hook function. The first argument to this function is a TestContext object. If the hook uses callbacks, the callback function is passed as the second argument.

    @param options

    Configuration options for the hook.

  • message: string
    ): void;

    This function is used to write diagnostics to the output. Any diagnostic information is included at the end of the test's results. This function does not return a value.

    test('top level test', (t) => {
  t.diagnostic('A diagnostic message');
});
    @param message

    Message to be reported.

  • count: number,
    options?: TestContextPlanOptions
    ): void;

    This function is used to set the number of assertions and subtests that are expected to run within the test. If the number of assertions and subtests that run does not match the expected count, the test will fail.

    Note: To make sure assertions are tracked, t.assert must be used instead of assert directly.

    test('top level test', (t) => {
  t.plan(2);
  t.assert.ok('some relevant assertion here');
  t.test('subtest', () => {});
});

    When working with asynchronous code, the plan function can be used to ensure that the correct number of assertions are run:

    test('planning with streams', (t, done) => {
  function* generate() {
    yield 'a';
    yield 'b';
    yield 'c';
  }
  const expected = ['a', 'b', 'c'];
  t.plan(expected.length);
  const stream = Readable.from(generate());
  stream.on('data', (chunk) => {
    t.assert.strictEqual(chunk, expected.shift());
  });

  stream.on('end', () => {
    done();
  });
});

    When using the wait option, you can control how long the test will wait for the expected assertions. For example, setting a maximum wait time ensures that the test will wait for asynchronous assertions to complete within the specified timeframe:

    test('plan with wait: 2000 waits for async assertions', (t) => {
  t.plan(1, { wait: 2000 }); // Waits for up to 2 seconds for the assertion to complete.

  const asyncActivity = () => {
    setTimeout(() => {
         *       t.assert.ok(true, 'Async assertion completed within the wait time');
    }, 1000); // Completes after 1 second, within the 2-second wait time.
  };

  asyncActivity(); // The test will pass because the assertion is completed in time.
});

    Note: If a wait timeout is specified, it begins counting down only after the test function finishes executing.

  • shouldRunOnlyTests: boolean
    ): void;

    If shouldRunOnlyTests is truthy, the test context will only run tests that have the only option set. Otherwise, all tests are run. If Node.js was not started with the --test-only command-line option, this function is a no-op.

    test('top level test', (t) => {
  // The test context can be set to run subtests with the 'only' option.
  t.runOnly(true);
  return Promise.all([
    t.test('this subtest is now skipped'),
    t.test('this subtest is run', { only: true }),
  ]);
});
    @param shouldRunOnlyTests

    Whether or not to run only tests.

  • message?: string
    ): void;

    This function causes the test's output to indicate the test as skipped. If message is provided, it is included in the output. Calling skip() does not terminate execution of the test function. This function does not return a value.

    test('top level test', (t) => {
  // Make sure to return here as well if the test contains additional logic.
  t.skip('this is skipped');
});
    @param message

    Optional skip message.

  • message?: string
    ): void;

    This function adds a TODO directive to the test's output. If message is provided, it is included in the output. Calling todo() does not terminate execution of the test function. This function does not return a value.

    test('top level test', (t) => {
  // This test is marked as `TODO`
  t.todo('this is a todo');
});
    @param message

    Optional TODO message.

  • condition: () => T,
    options?: TestContextWaitForOptions
    ): Promise<Awaited<T>>;

    This method polls a condition function until that function either returns successfully or the operation times out.

    @param condition

    An assertion function that is invoked periodically until it completes successfully or the defined polling timeout elapses. Successful completion is defined as not throwing or rejecting. This function does not accept any arguments, and is allowed to return any value.

    @param options

    An optional configuration object for the polling operation.

    @returns

    Fulfilled with the value returned by condition.