better error handling

tests/includes/datastream_validators.inc

@@ -128,6 +128,7 @@ abstract class DatastreamValidator extends IslandoraTestUtilityClass {
    * fails to $this->passes and/or $this->fails.
    */
   public function runValidators() {
+    if ($this->object[$this->datastream]) {
       $methods = get_class_methods($this);
       foreach ($methods as $method) {
         if (substr($method, 0, 6) === 'assert') {
@@ -135,6 +136,10 @@ abstract class DatastreamValidator extends IslandoraTestUtilityClass {
         }
       }
     }
+    else {
+      $this->addResult(FALSE, "Unable to load the requested datastream {$this->datastream} from object {$this->object->id}.");
+    }
+  }
 
   /**
    * Returns an array of IslandoraTestUtilityResults.