jest-t-assert

jest-t-assert

Use tape style assertions with Jest. The assertions are very similar to AVA.

If you just want to migrate from AVA to Jest you should use jest-codemods instead.

Usage

import test from 'jest-t-assert';

test('a test case', t => {
  t.true(2 < 10);
  t.truthy(1);
  t.not(2, '2');
  t.deepEqual([1, 2], [1, 2]);
  t.throws(() => {
    throw new Error('This function throws');
  });
  t.snapshot({ a: 1, b: 'ok' });
});

You can also import t directly if you only want to use the assertions without the test wrapper. This doesn't break existing tests that use Jest's callback mode, where you call done(), which is passed as the first argument to the test function.

import { t } from 'jest-t-assert';

test('only using the assertions from `t`', () => {
  t.true(2 < 10);
  t.truthy(1);
  t.not(2, '2');
  t.deepEqual([1, 2], [1, 2]);
  t.throws(() => {
    throw new Error('This function throws');
  });
  t.snapshot({ a: 1, b: 'ok' });
});

Asynchronous tests

Jest supports returning a promise from the test, so you can do the assertions in the .then calls.

import test from 'jest-t-assert';

test('promise resolves with the correct value', t => {
  return Promise.resolve('value').then(val => t.is(val, 'value'));
});

test('using async/await', async t => {
  const val = await Promise.resolve('value');
  t.is(val, 'value');
  // await directly
  t.is(await Promise.resolve('value'), 'value');
});

If you need to use the callback mode you have to use test.cb, which requires you to end the test manually by calling t.end(). It is highly recommended to use promises and async / await instead of the callback mode.

import test from 'jest-t-assert';

test.cb('a callback', t => {
  t.plan(1);
  setTimeout(() => {
    t.pass();
    t.end();
  }, 2000);
});

API

test([title], fn)

Run a test. fn will receive t as the first argument, which provides the assertions.

test.cb([title], fn)

Run a test in callback mode. fn will receive t, which provides the usual assertions and additionally t.end(), which must be called to manually end the test. .cb can be chained with any of modifiers listed below.

test.only([title], fn)

Only run this test. All other tests in the test suite are skipped.

test.skip([title], fn)

Skip the test. Useful to avoid a failing test without removing it or commenting it out.

test.after(fn)

Runs fn after all tests in the test suite have completed.

test.afterEach(fn)

Runs fn after each test in the test suite has completed.

test.before(fn)

Runs fn before any test in the test suite is run.

test.beforeEach(fn)

Runs fn before each test in the test suite is run.

t

The argument passed to the callback of test, which is also exported as t.

t.end()

End the test. This is only available when using test.cb.

t.plan(count)

Plan how many assertions are used in the test. The test fails if the number of assertions differs from count.

t.pass()

An assertion that always passes.

t.fail()

An assertion that always fails.

t.true(actual)

Assert that actual is true.

t.false(actual)

Assert that actual is false.

t.truthy(actual)

Assert that actual is truthy.

t.falsy(actual)

Assert that actual is falsy.

t.is(actual, expected)

Assert that actual is equal to expected (based on ===).

t.not(actual, expected)

Assert that actual is not equal to expected (based on ===). The inverse of t.is(actual, expected).

t.deepEqual(actual, expected)

Assert that actual is deeply equal to expected. This recursively checks the equality of all fields.

t.notDeepEqual(actual, expected)

Assert that actual is not deeply equal to expected. This recursively checks the equality of all fields. The inverse of t.deepEqual(actual, expected).

t.throws(fn, [error])

Assert that fn throws an error. If error is provided, the thrown error must match it.

t.notThrows(fn)

Assert that fn does not throw an error. The inverse of t.throws(fn).

t.regex(actual, regex)

Assert that actual matches regex.

t.notRegex(actual, regex)

Assert that actual does not match regex. The inverse of t.regex(actual, regex).

t.snapshot(actual)

Assert that actual matches the most recent snapshot.