Add code coverage reports

Author: gloomy

.github/workflows/php.yml

@@ -46,3 +46,6 @@ jobs:
 
       - name: Run php unit tests
         run: composer run-script unit-tests
+
+      - name: Submit coverage report
+        run: bash <(curl -s https://codecov.io/bash)

phpunit.xml

@@ -18,4 +18,12 @@
             <directory suffix="Test.php">./tests/Unit</directory>
         </testsuite>
     </testsuites>
+    <logging>
+        <log type="coverage-clover" target="clover.xml"/>
+    </logging>
+    <filter>
+        <whitelist>
+            <directory>tests/Unit</directory>
+        </whitelist>
+    </filter>
 </phpunit>