Don't pass strings to isInstanceOf in the tests.
diff --git a/test/core_matchers_test.dart b/test/core_matchers_test.dart
index 7024894..5cd17da 100644
--- a/test/core_matchers_test.dart
+++ b/test/core_matchers_test.dart
@@ -177,9 +177,9 @@
   });
 
   test('isInstanceOf', () {
-    shouldFail(0, new isInstanceOf<String>('String'),
+    shouldFail(0, new isInstanceOf<String>(),
         "Expected: an instance of String Actual: <0>");
-    shouldPass('cow', new isInstanceOf<String>('String'));
+    shouldPass('cow', new isInstanceOf<String>());
   });
 
   group('Predicate Matchers', () {