Port ClassDB tests to use doctest

Extracted the most minimal core initialization functionality from
`setup()` and `setup2()` so that `ClassDB` could be tested properly
(input, audio, rendering, physics etc, are excluded).

Display and rendering servers/singletons are not initialized at all.

Due to the fact that most subsystems are disabled, fixed various crashes in the
process (in order):
- `AcceptDialog` OK/cancel swap behavior (used `DisplayServer` while
  `register_scene_types()`);
- `make_default_theme` which depends on `RenderingServer`;
- `XRServer` singleton access while calling `register_modules_types()`;
- hidden bug in a way joypads are cleaned up (MacOS and Linux only).

Removed manual `ClassDB` init/cleanup calls from `test_validate_testing.h`.

ClassDB tests:

Co-authored-by: Ignacio Etcheverry <ignalfonsore@gmail.com>

2 files changed, 87 insertions, 5 deletions

diff --git a/main/main.cpp b/main/main.cpp
index 1c02fcf939..e45162c0f3 100644
--- a/main/main.cpp
+++ b/main/main.cpp
@@ -369,16 +369,94 @@ void Main::print_help(const char *p_binary) {
 #endif
 }
 
+#ifdef TESTS_ENABLED
+// The order is the same as in `Main::setup()`, only core and some editor types
+// are initialized here. This also combines `Main::setup2()` initialization.
+Error Main::test_setup() {
+	OS::get_singleton()->initialize();
+
+	engine = memnew(Engine);
+
+	ClassDB::init();
+
+	register_core_types();
+	register_core_driver_types();
+
+	globals = memnew(ProjectSettings);
+
+	GLOBAL_DEF("debug/settings/crash_handler/message",
+			String("Please include this when reporting the bug on https://github.com/godotengine/godot/issues"));
+
+	// From `Main::setup2()`.
+	preregister_module_types();
+	preregister_server_types();
+
+	register_core_singletons();
+
+	register_server_types();
+	register_scene_types();
+
+#ifdef TOOLS_ENABLED
+	ClassDB::set_current_api(ClassDB::API_EDITOR);
+	EditorNode::register_editor_types();
+
+	ClassDB::set_current_api(ClassDB::API_CORE);
+#endif
+	register_platform_apis();
+
+	register_module_types();
+	register_driver_types();
+
+	ClassDB::set_current_api(ClassDB::API_NONE);
+
+	_start_success = true;
+
+	return OK;
+}
+// The order is the same as in `Main::cleanup()`.
+void Main::test_cleanup() {
+	ERR_FAIL_COND(!_start_success);
+
+	EngineDebugger::deinitialize();
+
+	ResourceLoader::remove_custom_loaders();
+	ResourceSaver::remove_custom_savers();
+
+#ifdef TOOLS_ENABLED
+	EditorNode::unregister_editor_types();
+#endif
+	unregister_driver_types();
+	unregister_module_types();
+	unregister_platform_apis();
+	unregister_scene_types();
+	unregister_server_types();
+
+	OS::get_singleton()->finalize();
+
+	if (globals) {
+		memdelete(globals);
+	}
+	if (engine) {
+		memdelete(engine);
+	}
+
+	unregister_core_driver_types();
+	unregister_core_types();
+
+	OS::get_singleton()->finalize_core();
+}
+#endif
+
 int Main::test_entrypoint(int argc, char *argv[], bool &tests_need_run) {
 #ifdef TESTS_ENABLED
 	for (int x = 0; x < argc; x++) {
 		if ((strncmp(argv[x], "--test", 6) == 0) && (strlen(argv[x]) == 6)) {
 			tests_need_run = true;
-			OS::get_singleton()->initialize();
-			StringName::setup();
+			// TODO: need to come up with different test contexts.
+			// Not every test requires high-level functionality like `ClassDB`.
+			test_setup();
 			int status = test_main(argc, argv);
-			StringName::cleanup();
-			// TODO: fix OS::singleton cleanup
+			test_cleanup();
 			return status;
 		}
 	}
diff --git a/main/main.h b/main/main.h
index 20c0bebefa..75a1c0d8cd 100644
--- a/main/main.h
+++ b/main/main.h
@@ -48,6 +48,10 @@ public:
 	static int test_entrypoint(int argc, char *argv[], bool &tests_need_run);
 	static Error setup(const char *execpath, int argc, char *argv[], bool p_second_phase = true);
 	static Error setup2(Thread::ID p_main_tid_override = 0);
+#ifdef TESTS_ENABLED
+	static Error test_setup();
+	static void test_cleanup();
+#endif
 	static bool start();
 
 	static bool iteration();
@@ -58,7 +62,7 @@ public:
 	static void cleanup();
 };
 
-// Test main override is for the testing behaviour
+// Test main override is for the testing behaviour.
 #define TEST_MAIN_OVERRIDE                                         \
 	bool run_test = false;                                         \
 	int return_code = Main::test_entrypoint(argc, argv, run_test); \