reg/tests: Add tests for trailing backslashes after the system key.

programs/reg/tests/add.c

@@ -268,6 +268,14 @@ static void test_add(void)
     verify_key(hkey, "keytest4");
     delete_key(hkey, "keytest4");
 
+    run_reg_exe("reg add HKCU\\ /v Value1 /t REG_SZ /d foo /f", &r);
+    todo_wine ok(r == REG_EXIT_FAILURE, "got exit code %d, expected 1\n", r);
+    todo_wine verify_reg_nonexist(HKEY_CURRENT_USER, "Value1");
+
+    run_reg_exe("reg add HKEY_CURRENT_USER\\ /v Value2 /t REG_SZ /d bar /f", &r);
+    todo_wine ok(r == REG_EXIT_FAILURE, "got exit code %d, expected 1\n", r);
+    todo_wine verify_reg_nonexist(HKEY_CURRENT_USER, "Value2");
+
     /* REG_NONE */
     run_reg_exe("reg add HKCU\\" KEY_BASE " /v none0 /d deadbeef /t REG_NONE /f", &r);
     ok(r == REG_EXIT_SUCCESS, "got exit code %d, expected 0\n", r);