Tests are located in the test/ directory and are organized using the following structure:

• test/
  • js/ - tests for JavaScript APIs.
  • cli/ - tests for commands, configs, and stdout.
  • bundler/ - tests for the transpiler/bundler.
  • regression/ - tests that reproduce a specific issue.
  • harness.ts - utility functions that can be imported from any test.

The tests in test/js/ directory are further categorized by the type of API.

• test/js/
  • bun/ - tests for Bun-specific APIs.
  • node/ - tests for Node.js APIs.
  • web/ - tests for Web APIs, like fetch().
  • first_party/ - tests for npm packages that are built-in, like undici.
  • third_party/ - tests for npm packages that are not built-in, but are popular, like esbuild.

To run a test, use Bun's built-in test command: bun test.

bun test # Run all tests bun test js/bun # Only run tests in a directory bun test sqlite.test.ts # Only run a specific test

If you encounter lots of errors, try running bun install, then trying again.

Tests are written in TypeScript (preferred) or JavaScript using Jest's describe(), test(), and expect() APIs.

import { describe, test, expect } from "bun:test"; import { gcTick } from "harness"; describe("TextEncoder", () => { test("can encode a string", async () => { const encoder = new TextEncoder(); const actual = encoder.encode("bun"); await gcTick(); expect(actual).toBe(new Uint8Array([0x62, 0x75, 0x6E])); }); });

If you are fixing a bug that was reported from a GitHub issue, remember to add a test in the test/regression/ directory.

// test/regression/issue/02005.test.ts import { it, expect } from "bun:test"; it("regex literal should work with non-latin1", () => { const text = "这是一段要替换的文字"; expect(text.replace(new RegExp("要替换"), "")).toBe("这是一段的文字"); expect(text.replace(/要替换/, "")).toBe("这是一段的文字"); });

In the future, a bot will automatically close or re-open issues when a regression is detected or resolved.

These tests live in various .zig files throughout Bun's codebase, leveraging Zig's builtin test keyword.

Currently, they're not run automatically nor is there a simple way to run all of them. We will make this better soon.

Test files should be written in TypeScript. The types in packages/bun-types should be updated to support all new APIs. Changes to the .d.ts files in packages/bun-types will be immediately reflected in test files; no build step is necessary.

Writing a test will often require using invalid syntax, e.g. when checking for errors when an invalid input is passed to a function. TypeScript provides a number of escape hatches here.

• // @ts-expect-error - This should be your first choice. It tells TypeScript that the next line should fail typechecking.
• // @ts-ignore - Ignore the next line entirely.
• // @ts-nocheck - Put this at the top of the file to disable typechecking on the entire file. Useful for autogenerated test files, or when ignoring/disabling type checks an a per-line basis is too onerous.