docs: explain testing, linting and commit linting

CONTRIBUTING.md

@@ -1,3 +1,55 @@
 Please see the [Contributing to Karma] guide for information on contributing to this project.
 
 [Contributing to Karma]: https://github.com/karma-runner/karma/blob/master/CONTRIBUTING.md
+
+# Pull Requests
+
+Before filing a PR, ensure that:
+
+* [ ] Tests pass.
+* [ ] Linting passes.
+* [ ] Commit linting passes.
+
+See more details in each subsection below.
+
+## Testing
+
+To run unit tests execute:
+
+```bash
+npm run unit-test
+```
+
+To run integration tests execute:
+
+```bash
+npm run integration-test
+```
+
+Tip: you can run both unit and integration tests in a single step via: `npm test`.
+
+## Linting
+
+To lint your contribution execute:
+
+```bash
+npm run lint
+```
+
+There are some lint problems that can be auto-fixed for you. Try the following command to trigger auto-fix:
+
+```bash
+npm run lint --fix
+```
+
+## Commit Linting
+
+We enforce [Angular's Commit Message Format] in our commit history. To verify that your commits are syntactically correct, execute:
+
+```bash
+npm run commitlint -- \
+  --verbose \
+  --from `git merge-base origin/master HEAD`
+```
+
+[Angular's Commit Message Format]: https://github.com/angular/angular/blob/master/CONTRIBUTING.md#commit