diff --git a/src/tests/strings_func.cpp b/src/tests/strings_func.cpp
new file mode 100644
--- /dev/null
+++ b/src/tests/strings_func.cpp
@@ -0,0 +1,52 @@
+/*
+ * This file is part of OpenTTD.
+ * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
+ * OpenTTD 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 OpenTTD. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/** @file strings_func.cpp Test functionality from strings_func. */
+
+#include "../stdafx.h"
+
+#include "../3rdparty/catch2/catch.hpp"
+
+#include "../strings_func.h"
+
+TEST_CASE("HaveDParamChanged")
+{
+	SetDParam(0, 0);
+	SetDParamStr(1, "some string");
+
+	std::vector<StringParameterBackup> backup;
+	CopyOutDParam(backup, 2);
+
+	CHECK(HaveDParamChanged(backup) == false);
+
+	/* A different parameter 0 (both string and numeric). */
+	SetDParam(0, 1);
+	CHECK(HaveDParamChanged(backup) == true);
+
+	SetDParamStr(0, "some other string");
+	CHECK(HaveDParamChanged(backup) == true);
+
+	/* Back to the original state, nothing should have changed. */
+	SetDParam(0, 0);
+	CHECK(HaveDParamChanged(backup) == false);
+
+	/* A different parameter 1 (both string and numeric). */
+	SetDParamStr(1, "some other string");
+	CHECK(HaveDParamChanged(backup) == true);
+
+	SetDParam(1, 0);
+	CHECK(HaveDParamChanged(backup) == true);
+
+	/* Back to the original state, nothing should have changed. */
+	SetDParamStr(1, "some string");
+	CHECK(HaveDParamChanged(backup) == false);
+
+	/* Changing paramter 2 should not have any effect, as the backup is only 2 long. */
+	SetDParam(2, 3);
+	CHECK(HaveDParamChanged(backup) == false);
+
+}