Add coverage information to tests, fix coverage of NodaValidationHelper

tests/NodaTimeSplitterTest.php

@@ -9,6 +9,8 @@ use PHPUnit\Framework\TestCase;
 
 /**
  * This script contains tests for the time name splitter.
+ *
+ * @covers \NodaTimeSplitter
  */
 final class NodaTimeSplitterTest extends TestCase {
     /**