user: Add a test for CreateWindowEx.

dlls/user/tests/win.c

@@ -137,8 +137,10 @@ static void test_parent_owner(void)
     trace( "main window %p main2 %p desktop %p child %p\n", hwndMain, hwndMain2, desktop, child );
 
     /* child without parent, should fail */
+    SetLastError(0xdeadbeef);
     test = CreateWindowExA(0, "ToolWindowClass", "Tool window 1",
                            WS_CHILD, 0, 0, 100, 100, 0, 0, 0, NULL );
+    todo_wine ok( GetLastError() == ERROR_TLW_WITH_WSCHILD, "CreateWindowExA should call SetLastError\n" );
     ok( !test, "WS_CHILD without parent created\n" );
 
     /* desktop window */