Use to indicate a type error

types/knockout/test/templatingBehaviors.ts

@@ -575,7 +575,8 @@ describe('Templating', function() {
 
         // Now set the observable to null and check it's treated like an empty array
         // (because how else should null be interpreted?)
-        myArray(null as any); // DefinitelyTyped note: while KO accepts this, I wouldn't consider it a well-typed usage of the API
+        // DefinitelyTyped note: while KO accepts this, I wouldn't consider it a well-typed usage of the API
+        myArray(null); // $ExpectError
         expect(testNode.childNodes[0].childNodes.length).toEqual(0);
     });