ci(test-optimization): run datadog-plugin-jest unit spec

`packages/datadog-plugin-jest/test/util.spec.js` is matched by
`test:plugins`' glob but no workflow set `PLUGINS=jest` for
`test:plugins:ci`; the existing `integration-jest` matrix runs
`integration-tests/jest/*.spec.js` only, which does not cover the
plugin package's own unit tests. The new joint check flagged it as
never reached.

Add a single `jest:` job invoking the `plugins/test` composite action.
`util.spec.js` is a pure unit test on `getFormattedJestTestParameters`
and `getJestSuitesToRun`, so no service containers or matrix axes are
needed beyond what `plugins/test` already covers (oldest-maintenance
and latest Node).

Restore the three fixture files (`test-to-run.js`, `test-to-skip.js`,
`test-unskippable.js`) under `packages/datadog-plugin-jest/test/fixtures/`
that `getJestSuitesToRun` reads via `isMarkedAsUnskippable`. They were
deleted alongside the other jest plugin specs when those moved to
integration tests, but `util.spec.js` was kept and silently broke
because no CI invocation reached it.

Author: BridgeAR

.github/workflows/test-optimization.yml

@@ -206,6 +206,19 @@ jobs:
           flags: test-optimization-jest-${{ matrix.version }}-${{ matrix.jest-version }}
           dd_api_key: ${{ steps.dd-sts.outputs.api_key }}
 
+  # Unit tests for `packages/datadog-plugin-jest`. The `integration-jest` matrix above only runs
+  # `integration-tests/jest/*.spec.js`, so this is the only CI invocation whose glob expands to
+  # cover `packages/datadog-plugin-jest/test/util.spec.js`.
+  jest:
+    runs-on: ubuntu-latest
+    permissions:
+      id-token: write
+    env:
+      PLUGINS: jest
+    steps:
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+      - uses: ./.github/actions/plugins/test
+
   integration-cucumber:
     strategy:
       fail-fast: false

eslint.config.mjs

@@ -802,6 +802,15 @@ export default [
       'mocha/no-pending-tests': 'off',
     },
   },
+  {
+    // jest-docblock's `@datadog {"unskippable": true}` tag reads as a malformed
+    // JSDoc type to `jsdoc/valid-types`. The shape is required by the plugin.
+    name: 'dd-trace/datadog-plugin-jest/fixtures',
+    files: ['packages/datadog-plugin-jest/test/fixtures/**/*.js'],
+    rules: {
+      'jsdoc/valid-types': 'off',
+    },
+  },
   {
     // CI-visibility retry fixtures intentionally call `this.retries(N)` to
     // exercise the dd-trace test-optimization retry code paths. The fixtures

packages/datadog-plugin-jest/test/fixtures/test-to-run.js

@@ -0,0 +1,8 @@
+'use strict'
+
+// Fixture for util.spec.js. `getJestSuitesToRun` reads this file to scan for
+// a `@datadog` docblock; the body of the suite is never executed.
+
+describe('test-to-run', () => {
+  it('is a placeholder fixture', () => {})
+})

packages/datadog-plugin-jest/test/fixtures/test-to-skip.js

@@ -0,0 +1,8 @@
+'use strict'
+
+// Fixture for util.spec.js. `getJestSuitesToRun` reads this file to scan for
+// a `@datadog` docblock; the body of the suite is never executed.
+
+describe('test-to-skip', () => {
+  it('is a placeholder fixture', () => {})
+})

packages/datadog-plugin-jest/test/fixtures/test-unskippable.js

@@ -0,0 +1,11 @@
+/**
+ * @datadog {"unskippable": true}
+ */
+'use strict'
+
+// Fixture for util.spec.js. `getJestSuitesToRun` reads this file to scan for
+// the `@datadog` docblock above; the body of the suite is never executed.
+
+describe('test-unskippable', () => {
+  it('is a placeholder fixture', () => {})
+})