function testIsValid_AddsErrorIfARequiredFieldValueIsAnEmptyString()
 {
     $f = new Tracker_FormElement_Field_ArtifactLinkTestVersion();
     $f->setReturnValue('isRequired', true);
     $a = new MockTracker_Artifact();
     $a->setReturnValue('getLastChangeset', false);
     $this->assertFalse($f->isValidRegardingRequiredProperty($a, ''));
     $this->assertTrue($f->hasErrors());
 }