Add coverage (#5)

* Add coverage

* Tweak coverage

* Tweak coverage

Author: barryvdh

.github/workflows/run-tests.yml

@@ -35,6 +35,7 @@ jobs:
       with:
         php-version: ${{ matrix.php }}
         extensions: mbstring
+        coverage: pcov
 
     - name: Install dependencies
       run: |
@@ -51,3 +52,7 @@ jobs:
     - name: Check PSR-12 Codestyle
       run: composer test
       if: matrix.os == 'ubuntu-latest'
+
+    - name: Check Code Coverage
+      run: php vendor/bin/phpunit --verbose --coverage-text
+      if: matrix.dependency-version == 'prefer-stable' && matrix.php == '8.1'