add coverage reporting

ot_core/.gitignore

@@ -3,3 +3,4 @@
 Build/testing-docker/.env
 composer.lock
 /var/
+/coverage/

ot_core/Tests/Build/UnitTests.xml

@@ -20,6 +20,18 @@
         </testsuite>
     </testsuites>
 
+    <filter>
+        <whitelist processUncoveredFilesFromWhitelist="true">
+            <directory suffix=".php">../../Classes</directory>
+            <exclude>
+            </exclude>
+        </whitelist>
+    </filter>
+
+    <logging>
+        <log type="coverage-html" target="../../coverage" lowUpperBound="35" highLowerBound="70"/>
+    </logging>
+
     <php>
         <!-- suppress deprecation warnings - set error reporting to: E_ALL & ~E_NOTICE & ~E_USER_ERROR & ~E_USER_WARNING & ~E_USER_NOTICE & ~E_STRICT & ~E_USER_DEPRECATED -->
         <ini name="error_reporting" value="12535"/>