jscript: Removed obsolete FIXME comments in tests and add relevant tests.

dlls/jscript/tests/lang.js

@@ -208,10 +208,13 @@ function argumentsTest() {
         return 1;
     });
 }
-/* FIXME: It seems that when function is called as an expression, instance object arguments is not set.
- * We currently always set it in Wine. */
+
 argumentsTest();
 
+(function callAsExprTest() {
+    ok(callAsExprTest.arguments === null, "callAsExprTest.arguments = " + callAsExprTest.arguments);
+})(1,2);
+
 tmp = (function() {1;})();
 ok(tmp === undefined, "tmp = " + tmp);
 tmp = eval("1;");