diff --git a/test/CLAUDE.md b/test/CLAUDE.md
index 8d63729452..ee22ea9f1b 100644
--- a/test/CLAUDE.md
+++ b/test/CLAUDE.md
@@ -16,9 +16,10 @@ Note that compiling Bun may take up to 2.5 minutes. It is slow!
 
 ## Testing style
 
-Use `bun:test` with files that end in `*.test.ts`.
+Use `bun:test` with files that end in `*.test.{ts,js,jsx,tsx,mjs,cjs}`. If it's a test/js/node/test/{parallel,sequential}/\*.js without a .test.extension, use `bun bd <file>` instead of `bun bd test <file>` since those expect exit code 0 and don't use bun's test runner.
 
-**Do not write flaky tests**. Unless explicitly asked, **never wait for time to pass in tests**. Always wait for the condition to be met instead of waiting for an arbitrary amount of time. **Never use hardcoded port numbers**. Always use `port: 0` to get a random port.
+- **Do not write flaky tests**. Unless explicitly asked, **never wait for time to pass in tests**. Always wait for the condition to be met instead of waiting for an arbitrary amount of time. **Never use hardcoded port numbers**. Always use `port: 0` to get a random port.
+- **Prefer concurrent tests over sequential tests**: When multiple tests in the same file spawn processes or write files, make them concurrent with `test.concurrent` or `describe.concurrent` unless it's very difficult to make them concurrent.
 
 ### Spawning processes
 
@@ -115,7 +116,7 @@ To create a repetitive string, use `Buffer.alloc(count, fill).toString()` instea
 ### Test Organization
 
 - Use `describe` blocks for grouping related tests
-- Regression tests go in `/test/regression/issue/` with issue number
+- Regression tests for specific issues go in `/test/regression/issue/${issueNumber}.test.ts`. If there's no issue number, do not put them in the regression directory.
 - Unit tests for specific features are organized by module (e.g., `/test/js/bun/`, `/test/js/node/`)
 - Integration tests are in `/test/integration/`