msvcrt/tests: Test _dup2 for failure when second arg is negative.

dlls/msvcrt/tests/file.c

@@ -1361,6 +1361,11 @@ static void test_unlink(void)
     rmdir("test_unlink");
 }
 
+void test_dup2(void)
+{
+    todo_wine ok(-1 == _dup2(0, -1), "expected _dup2 to fail when second arg is negative\n" );
+}
+
 START_TEST(file)
 {
     int arg_c;
@@ -1381,6 +1386,7 @@ START_TEST(file)
             ok(0, "invalid argument '%s'\n", arg_v[2]);
         return;
     }
+    test_dup2();
     test_file_inherit(arg_v[0]);
     test_file_write_read();
     test_chsize();