Auto-update snapshot tests if changing strings (#20)

The special incantation to update snapshots is tough to remember and non-obvious for many folks who are just updating text copy in the app. This makes the CI workflow auto-update snapshot tests on pull requests (not other pushes) where there were changes to the english strings.

It's possible this could make tests pass when they shouldn't (if other things that should not have changed were changed), so it also posts a comment to the PR if it had to update the snapshots that reminds a reviewer to check the snapshot changes.

.github/workflows/build-client.yml

@@ -17,6 +17,7 @@ concurrency:
 
 env:
   node-version: 18
+  english-strings: client/src/intl/en.json
 
 jobs:
   build:
@@ -31,6 +32,8 @@ jobs:
         uses: actions/setup-node@v4
         with:
           node-version: ${{ env.node-version }}
+          cache: npm
+          cache-dependency-path: client/package-lock.json
 
       - name: Install
         run: npm ci
@@ -55,22 +58,73 @@ jobs:
 
   test:
     runs-on: ubuntu-latest
+    needs:
+      - translations
     defaults:
       run:
         working-directory: client
+    permissions:
+      contents: write       # For commiting changes back to the current PR.
+      pull-requests: write  # For commenting on the PR.
     steps:
       - uses: actions/checkout@v4
+        with:
+          # The translation job may have committed some changes; use them!
+          ref: ${{ needs.translations.outputs.commit_hash }}
 
       - name: Use Node.js ${{ env.node-version }}
         uses: actions/setup-node@v4
         with:
           node-version: ${{ env.node-version }}
+          cache: npm
+          cache-dependency-path: client/package-lock.json
 
       - name: Install
         run: npm ci
 
+      # We want to know if this branch has changed the english strings, not
+      # just if the `translations` job had to update it, so we need this check.
+      - uses: dorny/paths-filter@v3
+        id: changes
+        with:
+          filters: |
+            english:
+              - ${{ env.english-strings }}
+
       - name: Unit tests
-        run: npm test
+        env:
+          update_snapshots: ${{ github.event_name == 'pull_request' && steps.changes.outputs.english == 'true' }}
+        run: |
+          if [ "${update_snapshots}" == 'true' ]; then
+            echo '⚠️ Updating snapshots as part of the test!'
+            echo '-----------------------------------------'
+            npm run test:update
+          else
+            npm test
+          fi
+
+      - name: Commit changes to Snapshots
+        uses: stefanzweifel/git-auto-commit-action@v5
+        id: commit
+        if: github.event_name == 'pull_request'
+        with:
+          commit_message: 'Auto-update snapshot tests'
+          file_pattern: '*.snap'
+
+      - name: Comment on the PR about changes
+        uses: thollander/actions-comment-pull-request@v3
+        if: steps.commit.outputs.changes_detected == 'true'
+        env:
+          commit_url: 'https://github.com/${{ github.repository }}/commit/${{ steps.commit.outputs.commit_hash }}'
+        with:
+          message: >
+            🚨 The "snapshot" tests in your PR have been automatically updated
+            because you changed some text in the app! **Make sure [the changes
+            to `.snap` files](${{ env.commit_url }}) are correct** and don’t
+            include other things that should *not* have changed.
+
+            You can also update snapshot tests yourself when working locally by
+            running `npm run test:update` on the command line.
 
   lint:
     runs-on: ubuntu-latest
@@ -84,6 +138,8 @@ jobs:
         uses: actions/setup-node@v4
         with:
           node-version: ${{ env.node-version }}
+          cache: npm
+          cache-dependency-path: client/package-lock.json
 
       - name: Install
         run: npm ci
@@ -109,13 +165,18 @@ jobs:
     permissions:
       contents: write       # For commiting changes back to the current PR.
       pull-requests: write  # For commenting on the PR.
+    outputs:
+      changed: ${{ steps.commit-strings.outputs.changes_detected == 'true' }}
+      commit_hash: ${{ steps.commit-strings.outputs.commit_hash }}
     steps:
       - uses: actions/checkout@v4
 
       - name: Use Node.js ${{ env.node-version }}
         uses: actions/setup-node@v4
         with:
           node-version: ${{ env.node-version }}
+          cache: npm
+          cache-dependency-path: client/package-lock.json
 
       - name: Install
         run: npm ci
@@ -124,20 +185,22 @@ jobs:
         if: github.event_name == 'pull_request'
         run: npm run intl:extract
 
-      - uses: stefanzweifel/git-auto-commit-action@v5
+      - name: Commit changes to English strings
+        uses: stefanzweifel/git-auto-commit-action@v5
         id: commit-strings
         if: github.event_name == 'pull_request'
         with:
           commit_message: 'Auto-update en.json from component source code'
-          file_pattern: 'client/src/intl/en.json'
+          file_pattern: '${{ env.english-strings }}'
 
-      - uses: thollander/actions-comment-pull-request@v3
+      - name: Comment on the PR about changes
+        uses: thollander/actions-comment-pull-request@v3
         if: steps.commit-strings.outputs.changes_detected == 'true'
         with:
           message: >
             :wave: FYI, your PR has been automatically updated with changes to
-            `client/src/intl/en.json`, which contains all the translatable text
-            from the application (probably because you made changes to
+            `${{ env.english-strings }}`, which contains all the translatable
+            text from the application (probably because you made changes to
             the text of a component without updating this file).
 
       - name: Check Spanish translations