Workflows: Prime a WP install and skip install for the actual test ru…

…n. (#256)

The PHPUnit test workflow now performs a dummy run to prime the WordPress install for tests.

When this completes, the actual test run is performed, with the `WP_TESTS_SKIP_INSTALL` environment variable set to `1`.

Since many of the tests must run in separate processes, this change means that installation occurs only once, instead of once per process.

.github/workflows/phpunit-tests.yml

@@ -41,5 +41,10 @@ jobs:
       - name: Setup tests
         run: bash bin/install-wp-tests.sh wordpress_tests root root 127.0.0.1 latest true
 
+      - name: Prime the WordPress install for tests
+        id: prime-tests
+        run: XDEBUG_MODE=off phpunit${{ matrix.multisite && ' -c tests/phpunit/multisite.xml' || '' }} --filter gha_install_wp > /dev/null 2>&1
+
       - name: Run tests
-        run: XDEBUG_MODE=off phpunit${{ matrix.multisite && ' -c tests/phpunit/multisite.xml' || '' }}
+        if: steps.prime-tests.outcome == 'success'
+        run: XDEBUG_MODE=off WP_TESTS_SKIP_INSTALL=1 phpunit${{ matrix.multisite && ' -c tests/phpunit/multisite.xml' || '' }}