Issue 6221 - Add native tests.

test/compiled/String.cpp

+/*
+ * This file is part of Adblock Plus <https://adblockplus.org/>,
+ * Copyright (C) 2006-present eyeo GmbH
+ *
+ * Adblock Plus is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 3 as
+ * published by the Free Software Foundation.
+ *
+ * Adblock Plus is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <string>
+#include "gtest/gtest.h"
+#include "compiled/String.h"
+
+TEST(TestString, DependentString)
+{
+  DependentString s;
+  EXPECT_TRUE(s.is_invalid());
+
+  DependentString s2(s);
+  EXPECT_TRUE(s2.is_invalid());
+}
+
+TEST(TestString, OwnedString)

[sergei, 2018/01/29 13:38:44]

It's not important for this change set but in general I would rather prefer
something like
TEST(OwnedString, ConstructingInvalidString)

[hub, 2018/01/29 16:57:46]

Done.

+{
+  OwnedString s;
+  EXPECT_TRUE(s.is_invalid());
+
+  // Valid string
+  OwnedString s2(2);
+  EXPECT_FALSE(s2.is_invalid());
+
+  // Ensure we still have an invalid string.
+  OwnedString s3(s);
+  EXPECT_TRUE(s3.is_invalid());
+
+  // Empty valid string lead to valid string.
+  OwnedString s4(u""_str);
+  EXPECT_FALSE(s4.is_invalid());
+}
+