composer install can only run after npm install as it uses npm package to fix the textdomain.

.travis.yml

@@ -37,8 +37,26 @@ matrix:
     env: WP_VERSION=latest WP_MULTISITE=0 RUN_PHPCS=1
   - name: "E2E tests"
     php: 7.4
-    script:
+    before_script:
+      - export PATH="$HOME/.composer/vendor/bin:$PATH"
+      - |
+        # Remove Xdebug for a huge performance increase:
+        if [ -f ~/.phpenv/versions/$(phpenv version-name)/etc/conf.d/xdebug.ini ]; then
+          phpenv config-rm xdebug.ini
+        else
+          echo "xdebug.ini does not exist"
+        fi
       - npm install
+      - composer install --no-dev
+      - |
+        # Install WP Test suite, install PHPUnit globally:
+        if [[ ! -z "$WP_VERSION" ]]; then
+          bash tests/bin/install.sh woocommerce_test root '' localhost $WP_VERSION
+          composer global require "phpunit/phpunit=5.7.*|7.5.*"
+        fi
+      - "/sbin/start-stop-daemon --start --quiet --pidfile /tmp/custom_xvfb_99.pid --make-pidfile --background --exec /usr/bin/Xvfb -- :99 -ac -screen 0 1280x1024x16"
+
+    script:
       - npm run build
       - docker-compose up --build -d
       - bash tests/bin/run-e2e-CI.sh