diff --git a/closure/goog/testing/testcase.js b/closure/goog/testing/testcase.js
index <HASH>..<HASH> 100644
--- a/closure/goog/testing/testcase.js
+++ b/closure/goog/testing/testcase.js
@@ -294,9 +294,10 @@ goog.testing.TestCase.prototype.onCompleteCallback_ = null;
 
 /**
  * Adds a new test to the test case.
- * @param {goog.testing.TestCase.Test} test The test to add.
+ * @param {!goog.testing.TestCase.Test} test The test to add.
  */
 goog.testing.TestCase.prototype.add = function(test) {
+  goog.asserts.assert(test);
   if (this.started) {
     throw Error('Tests cannot be added after execute() has been called. ' +
                 'Test: ' + test.name);
Fix type inconsistency found by upcoming compiler changes.
-------------
Created by MOE: <URL>