Add test for unescape_html().

tests/test_html_unescape.cpp

@@ -0,0 +1,54 @@
+/*  This file is part of mastodonpp.
+ *  Copyright © 2020 tastytea <tastytea@tastytea.de>
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU Affero General Public License as published by
+ *  the Free Software Foundation, version 3.
+ *
+ *  This program 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 Affero General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Affero General Public License
+ *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "helpers.hpp"
+
+#include <catch.hpp>
+
+#include <exception>
+#include <string>
+
+namespace mastodonpp
+{
+
+using std::string;
+
+SCENARIO ("mastodonpp::html_unescape()")
+{
+    bool exception = false;
+
+    WHEN ("html_unescape() is called.")
+    {
+        string result;
+        try
+        {
+            result = unescape_html("2&euro; = 2&#8364; = 2&#x20ac;");
+        }
+        catch (const std::exception &e)
+        {
+            exception = true;
+        }
+
+        THEN ("No exception is thrown")
+            AND_THEN("Result is as expected.")
+        {
+            REQUIRE_FALSE(exception);
+            REQUIRE(result == "2€ = 2€ = 2€");
+        }
+    }
+}
+
+} // namespace mastodonpp