This GitHub action runs a repo's vdiff tests. If the tests fail, a draft PR will be opened with the new goldens against the branch/PR that triggered the action. If they pass, any open golden PRs for that branch/PR will be closed.

More specifically, this action will:

• Cleanup abandoned golden PRs
• Grab the current golden images and set them up for the test run
• Run the vdiff tests and display the results in a custom commit status (including error messages, a link to the golden PR, etc.)
  • If failures occur, it will open/update the corresponding golden PR with the new goldens and link to the report
  • If the tests pass, it will close the corresponding golden PR if it exists

Typically this action is triggered from a workflow that runs on pull requests, ensuring that new code changes did not cause unexpected visual changes before they are merged.

Here's a sample workflow:

name: vdiff
on: pull_request
jobs:
  vdiff:
    timeout-minutes: 10
    runs-on: ubuntu-latest
    steps:
      - uses: Brightspace/third-party-actions@actions/checkout
      - uses: Brightspace/setup-node@main
        with:
          node-version-file: .nvmrc
          cache: 'npm'
      - name: Install dependencies
        run: npm ci
      - name: vdiff Tests
        uses: BrightspaceUI/actions/vdiff@main
        with:
          aws-access-key-id: ${{ secrets.AWS_ACCESS_KEY_ID }}
          aws-secret-access-key: ${{ secrets.AWS_SECRET_ACCESS_KEY }}
          aws-session-token: ${{ secrets.AWS_SESSION_TOKEN }}
          github-token: ${{ secrets.GITHUB_TOKEN }}

General Inputs:

• aws-access-key-id: Access key id for the role that will assume the vdiff role - see setup details below.
• aws-secret-access-key: Access key secret for the role that will assume the vdiff role - see setup details below.
• aws-session-token: Session token for the role that will assume the vdiff role - see setup details below.
• draft-pr (default: true): Whether to open the golden PR as a draft PR.
• github-token: Token used to cleanup branches and open the golden PR. This does not need admin privileges, so the standard GITHUB_TOKEN that's available can be used.
• vdiff-branch-prefix (default: ghworkflow/vdiff): Prefix for vdiff branches.

d2l-test-runner Inputs:

• test-chrome: Set --chrome flag to run vdiff tests in Chromium. If no browser flags are set, the default d2l-test-runner browser(s) for vdiff will be used.
• test-config: Set --config flag with d2l-test-runner config location.
• test-files: Set the --files flag with the pattern of vdiff tests to run.
• test-firefox: Set --firefox flag to run vdiff tests in Firefox. If no browser flags are set, the default d2l-test-runner browser(s) for vdiff will be used.
• test-safari: Set --safari flag to run vdiff tests in Webkit. If no browser flags are set, the default d2l-test-runner browser(s) for vdiff will be used.
• test-timeout: Set the --timeout flag with the timeout threshold for vdiff tests (in ms).

See the @brightspace-ui/testing repo's README to learn more about these flags.

Notes:

• You can also run this action in the release workflow to confirm the main branch is in a good state before releasing. If there's a problem, a PR will be opened against main to get the goldens back in the expected state. This mostly comes down to a time versus risk trade-off - the risk of things getting out of sync may be lower than the time taken to run the vdiff tests every release.
• You can use the standard GITHUB_TOKEN that exists automatically, but will need to set up the AWS secrets.

In order to have the AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY and AWS_SESSION_TOKEN secrets available in a repo, add that to the repo's setup in repo-settings.

If the repo has a CODEOWNERS file, it may not be desirable to have the vdiff pull requests set up with the same restrictions as other PRs. Golden PRs are usually opened against a branch that will be reviewed later by a code owner anyways. To remove the code owner restriction on these golden PRs, add the following to the CODEOWNERS file:

*       @<some_team> <some_username>
golden/
.vdiff.json

For more info on setting up and writing vdiff tests, refer to the @brightspace-ui/testing repo documentation.

New versions of @brightspace-ui/testing may include bumps to the browser versions running the tests. When those are updated, it often results in minor changes to the visual diff images.

To avoid blocking all PRs when the library updates until the new goldens are investigated and merged, we recommend committing the package-lock.json file and setting up the update-package-lock workflow to keep it up to date.