This guide demonstrates how to use the concurrentTestGlob option to selectively run tests concurrently based on file naming patterns.

Project Structure

my-project/
├── bunfig.toml
├── tests/
│   ├── unit/
│   │   ├── math.test.ts          # Sequential
│   │   └── utils.test.ts         # Sequential
│   └── integration/
│       ├── concurrent-api.test.ts     # Concurrent
│       └── concurrent-database.test.ts # Concurrent

Configuration

Configure your bunfig.toml to run test files with "concurrent-" prefix concurrently:

[test]
# Run all test files with "concurrent-" prefix concurrently
concurrentTestGlob = "**/concurrent-*.test.ts"

Test Files

Unit Test (Sequential)

Sequential tests are good for tests that share state or have specific ordering requirements:

import { test, expect } from "bun:test";

// These tests run sequentially by default
let sharedState = 0;

test("addition", () => {
  sharedState = 5 + 3;
  expect(sharedState).toBe(8);
});

test("uses previous state", () => {
  // This test depends on the previous test's state
  expect(sharedState).toBe(8);
});

Integration Test (Concurrent)

Tests in files matching the glob pattern automatically run concurrently:

import { test, expect } from "bun:test";

// These tests automatically run concurrently due to filename matching the glob pattern.
// Using test() is equivalent to test.concurrent() when the file matches concurrentTestGlob.
// Each test is independent and can run in parallel.

test("fetch user data", async () => {
  const response = await fetch("/api/user/1");
  expect(response.ok).toBe(true);
});

// can also use test.concurrent() for explicitly marking it as concurrent
test.concurrent("fetch posts", async () => {
  const response = await fetch("/api/posts");
  expect(response.ok).toBe(true);
});

// can also use test.serial() for explicitly marking it as sequential
test.serial("fetch comments", async () => {
  const response = await fetch("/api/comments");
  expect(response.ok).toBe(true);
});

Running Tests

# Run all tests - concurrent-*.test.ts files will run concurrently
bun test

# Override: Force ALL tests to run concurrently
# Note: This overrides bunfig.toml and runs all tests concurrently, regardless of glob
bun test --concurrent

# Run only unit tests (sequential)
bun test tests/unit

# Run only integration tests (concurrent due to glob pattern)
bun test tests/integration

Benefits

1. Gradual Migration: Migrate to concurrent tests file by file by renaming them
2. Clear Organization: File naming convention indicates execution mode
3. Performance: Integration tests run faster in parallel
4. Safety: Unit tests remain sequential where needed
5. Flexibility: Easy to change execution mode by renaming files

Migration Strategy

To migrate existing tests to concurrent execution:

1. Start with independent integration tests - These typically don't share state
2. Rename files to match the glob pattern: mv api.test.ts concurrent-api.test.ts
3. Verify tests still pass - Run bun test to ensure no race conditions
4. Monitor for shared state issues - Watch for flaky tests or unexpected failures
5. Continue migrating stable tests incrementally - Don't rush the migration

Tips

• Use descriptive prefixes: concurrent-, parallel-, async-
• Keep related sequential tests together in the same directory
• Document why certain tests must remain sequential with comments
• Use test.concurrent() for fine-grained control in sequential files (Note: In files matched by concurrentTestGlob, plain test() already runs concurrently)

Multiple Patterns

You can specify multiple patterns for different test categories:

[test]
concurrentTestGlob = [
  "**/integration/*.test.ts",
  "**/e2e/*.test.ts",
  "**/concurrent-*.test.ts"
]

This configuration will run tests concurrently if they match any of these patterns:

• All tests in integration/ directories
• All tests in e2e/ directories
• All tests with concurrent- prefix anywhere in the project