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Bun has a built-in test runner with a Jest-like expect API.
To use it, run the bun test command from your project directory. The test runner will recursively search for all files in the directory that match the following patterns and execute the tests they contain.
File Tree
*.test.{js|jsx|ts|tsx}
*_test.{js|jsx|ts|tsx}
*.spec.{js|jsx|ts|tsx}
*_spec.{js|jsx|ts|tsx}
Here’s what the output of a typical test run looks like. In this case, there are three tests files (test.test.js, test2.test.js, and test3.test.js) containing two tests each (add and multiply).
terminal
bun test

test.test.js:
✓ add [0.87ms]
✓ multiply [0.02ms]

test2.test.js:
✓ add [0.72ms]
✓ multiply [0.01ms]

test3.test.js:
✓ add [0.54ms]
✓ multiply [0.01ms]

 6 pass
 0 fail
 6 expect() calls
Ran 6 tests across 3 files. [9.00ms]
To only run certain test files, pass a positional argument to bun test. The runner will only execute files that contain that argument in their path.
terminal
bun test test3

test3.test.js:
✓ add [1.40ms]
✓ multiply [0.03ms]

 2 pass
 0 fail
 2 expect() calls
Ran 2 tests across 1 files. [15.00ms]
All tests have a name, defined using the first parameter to the test function. Tests can also be grouped into suites with describe. 
import {test, expect, describe} from 'bun:test';

describe('math', () => {
	test('add', () => {
		expect(2 + 2).toEqual(4);
	});

	test('multiply', () => {
		expect(2 * 2).toEqual(4);
	});
});
To filter which tests are executed by name, use the -t/--test-name-pattern flag. Adding -t add will only run tests with “add” in the name. This works with test names defined with test or test suite names defined with describe.
terminal
bun test -t add

test.test.js:
✓ add [1.79ms]
» multiply

test2.test.js:
✓ add [2.30ms]
» multiply

test3.test.js:
✓ add [0.32ms]
» multiply

 3 pass
 3 skip
 0 fail
 3 expect() calls
Ran 6 tests across 3 files. [59.00ms]
See Docs > Test Runner for complete documentation on the test runner.
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