diff --git a/src/tests/CMakeLists.txt b/src/tests/CMakeLists.txt
index ce33de8609..9a01d4e8fe 100644
--- a/src/tests/CMakeLists.txt
+++ b/src/tests/CMakeLists.txt
@@ -5,4 +5,5 @@ add_test_files(
     strings_func.cpp
     test_main.cpp
     test_script_admin.cpp
+    test_window_desc.cpp
 )
diff --git a/src/tests/test_window_desc.cpp b/src/tests/test_window_desc.cpp
new file mode 100644
index 0000000000..8421a9dc34
--- /dev/null
+++ b/src/tests/test_window_desc.cpp
@@ -0,0 +1,49 @@
+/*
+ * 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 test_window_desc.cpp Test WindowDescs for valid widget parts. */
+
+#include "../stdafx.h"
+
+#include "../3rdparty/catch2/catch.hpp"
+
+#include "../window_gui.h"
+
+/**
+ * List of WindowDescs. Defined in window.cpp but not exposed as this unit-test is the only other place that needs it.
+ * WindowDesc is a self-registering class so all WindowDescs will be included in the list.
+ */
+extern std::vector<WindowDesc*> *_window_descs;
+
+TEST_CASE("WindowDesc - ini_key uniqueness")
+{
+	std::set<std::string> seen;
+
+	for (const WindowDesc *window_desc : *_window_descs) {
+
+		if (window_desc->ini_key == nullptr) continue;
+
+		CAPTURE(window_desc->ini_key);
+		CHECK((seen.find(window_desc->ini_key) == std::end(seen)));
+
+		seen.insert(window_desc->ini_key);
+	}
+}
+
+TEST_CASE("WindowDesc - ini_key validity")
+{
+	const WindowDesc *window_desc = GENERATE(from_range(std::begin(*_window_descs), std::end(*_window_descs)));
+
+	bool has_inikey = window_desc->ini_key != nullptr;
+	bool has_widget = std::any_of(window_desc->nwid_begin, window_desc->nwid_end, [](const NWidgetPart &part) { return part.type == WWT_DEFSIZEBOX || part.type == WWT_STICKYBOX; });
+
+	INFO(fmt::format("{}:{}", window_desc->file, window_desc->line));
+	CAPTURE(has_inikey);
+	CAPTURE(has_widget);
+
+	CHECK((has_widget == has_inikey));
+}
diff --git a/src/window.cpp b/src/window.cpp
index de514ec8d5..2047a6efd7 100644
--- a/src/window.cpp
+++ b/src/window.cpp
@@ -96,7 +96,7 @@ SpecialMouseMode _special_mouse_mode; ///< Mode of the mouse.
  * List of all WindowDescs.
  * This is a pointer to ensure initialisation order with the various static WindowDesc instances.
  */
-static std::vector<WindowDesc*> *_window_descs = nullptr;
+std::vector<WindowDesc*> *_window_descs = nullptr;
 
 /** Config file to store WindowDesc */
 std::string _windows_file;