2.1.2.2. Running Builds/Tests on Pull Requests & Merges

2.1.2.2. Running Builds/Tests on Pull Requests & Merges

Catching bugs before code merges to the main branch prevents broken builds from blocking the entire team. The pattern: every pull request triggers a build-and-test cycle, and the PR can't be merged until tests pass.

With CodeCommit: Configure an EventBridge rule that matches pullRequestCreated and pullRequestSourceBranchUpdated events. The rule triggers a CodeBuild project that checks out the PR branch, runs tests, and posts the result back as a PR comment via the CodeCommit API.

With GitHub/Bitbucket: CodePipeline V2 supports triggers on pull request events via CodeConnections. Alternatively, use GitHub Actions or Bitbucket Pipelines to call CodeBuild directly via the aws codebuild start-build API.

Build Badge pattern: CodeBuild generates a badge URL that shows pass/fail status. Embed this in your repository README to give the team instant visibility into build health. Enable it in the CodeBuild project settings.

Merge gating: Combine CodeCommit approval rules (require N approvals + successful build) or GitHub branch protection rules (require status checks to pass) to enforce quality gates. A common pattern requires:

1. At least one peer approval
2. All CI tests passing
3. No merge conflicts with the target branch

Separation of duties for IaC pipelines: the PR approval gives four-eyes review of the code, a manual approval action before the deploy stage gates the release, distinct IAM roles for build and deploy keep the author from shipping alone, and CloudTrail records every approval and deploy call.

Exam Trap: CodePipeline V1 doesn't support PR-based triggers — it only triggers on pushes to a configured branch. If the exam asks about running tests on pull requests, the answer involves EventBridge + CodeBuild directly (not CodePipeline), unless the scenario specifies Pipeline V2.

💡 Tip: Run a lighter test suite on PR builds (unit + lint) and the full suite on merge to main. This keeps PR feedback under 5 minutes while maintaining thorough validation on the main branch.