Replace the broken test suite with working GdUnit4 tests

The previous tests never compiled: they used GUT's assert functions,
Godot 3 APIs and reassigned autoload functions, so no test ran.

- 90 tests: unit tests for the playlist, songs, player scoring, time
  formatting, search and the server client, plus integration tests
  that run MainWindow and SyncWindow against a fake server
- Keybind tests check that Alt+<number> and Ctrl+Alt+<number> keep
  following the player rows while players are added and removed
- run_tests.sh finds Godot and runs the suite headless (~10 seconds)
- CI runs the tests before the build job in gitea-build.yaml; the
  separate test.yml used a GitHub action that does not exist
- GdUnit4 is committed instead of ignored, since the project enables
  it, and .gitea/ is no longer ignored
- Exported builds leave out tests/ and addons/gdUnit4/

tests/integration/test_sync_window.gd

@@ -0,0 +1,145 @@
+extends GdUnitTestSuite
+
+var _server: FakeHttpTransport
+var _snapshot: AutoloadSnapshot
+var _runner: GdUnitSceneRunner
+var _window: Control
+
+
+func before_test() -> void:
+    _snapshot = AutoloadSnapshot.take([Settings])
+    Settings.currently_syncing = false
+    _server = FakeHttpTransport.new().install()
+    _server.respond_bytes("/sync", PackedByteArray())
+    _runner = scene_runner("res://SyncWindow.tscn")
+    _window = _runner.scene()
+
+
+func after_test() -> void:
+    _server.uninstall()
+    _snapshot.restore()
+
+
+func _node(unique_name: String) -> Control:
+    return _window.get_node("%" + unique_name)
+
+
+func _finish_sync(result: Dictionary) -> void:
+    _server.respond_json("/sync/progress", result)
+    _runner.invoke("_on_sync_timeout")
+
+
+func _empty_result() -> Dictionary:
+    return {
+        "soundtracks_added": [],
+        "soundtracks_re_added": [],
+        "soundtracks_changed_title": {},
+        "soundtracks_changed_content": [],
+        "soundtracks_removed": [],
+        "catched_errors": [],
+        "total_time": "00:00:03",
+    }
+
+
+func test_start_sync_asks_server_and_shows_progress() -> void:
+    monitor_signals(_window, false)
+
+    _runner.invoke("start_sync")
+
+    assert_array(_server.requested_paths).contains_exactly(["/sync"])
+    assert_bool(Settings.currently_syncing).is_true()
+    assert_bool(_node("ProgressHBoxContainer").visible).is_true()
+    assert_str(_node("SyncTitleLabel").text).is_equal("Sync in Progress")
+    await assert_signal(_window).is_emitted("sync_started")
+
+
+func test_start_sync_does_nothing_while_already_syncing() -> void:
+    Settings.currently_syncing = true
+
+    _runner.invoke("start_sync")
+
+    assert_array(_server.requested_paths).is_empty()
+
+
+func test_progress_updates_progress_bar() -> void:
+    _runner.invoke("start_sync")
+    _server.respond_json("/sync/progress", {"progress": "42", "time_spent": "00:00:12"})
+
+    _runner.invoke("_on_sync_timeout")
+
+    assert_float(_node("SyncProgressBar").value).is_equal(42.0)
+    assert_str(_node("SyncTime").text).is_equal("00:00:12")
+
+
+func test_finished_sync_shows_only_sections_with_changes() -> void:
+    _runner.invoke("start_sync")
+    monitor_signals(_window, false)
+    var result: Dictionary = _empty_result()
+    result.soundtracks_added = ["Chrono Cross", "Xenogears"]
+    result.soundtracks_removed = ["Bad Rip"]
+
+    _finish_sync(result)
+
+    assert_bool(_node("SoundtracksAddedVBox").visible).is_true()
+    assert_bool(_node("SoundtracksRemovedVBox").visible).is_true()
+    assert_bool(_node("SoundtracksReAddedVBox").visible).is_false()
+    assert_bool(_node("SoundtracksChangedTitleVBox").visible).is_false()
+    assert_bool(_node("NoChangesLabel").visible).is_false()
+    # Header plus one label per soundtrack
+    assert_int(_node("SoundtracksAddedVBox").get_child_count()).is_equal(3)
+    assert_str(_node("SyncTime").text).is_equal("Total time: 00:00:03")
+    assert_bool(Settings.currently_syncing).is_false()
+    await assert_signal(_window).is_emitted("sync_finished")
+
+
+func test_separator_shown_only_between_visible_sections() -> void:
+    _runner.invoke("start_sync")
+    var result: Dictionary = _empty_result()
+    result.soundtracks_added = ["Chrono Cross"]
+    result.soundtracks_removed = ["Bad Rip"]
+
+    _finish_sync(result)
+
+    assert_bool(_node("SoundtracksAddedSeparator").visible).is_true()
+    assert_bool(_node("SoundtracksRemovedSeparator").visible).is_false()
+
+
+func test_changed_titles_list_old_and_new_title() -> void:
+    _runner.invoke("start_sync")
+    var result: Dictionary = _empty_result()
+    result.soundtracks_changed_title = {"FF7": "Final Fantasy VII"}
+
+    _finish_sync(result)
+
+    var vbox: Control = _node("SoundtracksChangedTitleVBox")
+    assert_bool(vbox.visible).is_true()
+    assert_str((vbox.get_child(1) as Label).text).is_equal(
+            "FF7\nchanged title to\nFinal Fantasy VII")
+
+
+func test_no_changes_shows_no_changes_label() -> void:
+    _runner.invoke("start_sync")
+
+    _finish_sync(_empty_result())
+
+    assert_bool(_node("NoChangesLabel").visible).is_true()
+
+
+func test_errors_are_listed() -> void:
+    _runner.invoke("start_sync")
+    var result: Dictionary = _empty_result()
+    result.catched_errors = ["Could not read tags in broken.mp3"]
+
+    _finish_sync(result)
+
+    assert_bool(_node("CatchedErrorsVBox").visible).is_true()
+
+
+func test_reopening_after_sync_shows_result_without_syncing_again() -> void:
+    _runner.invoke("start_sync")
+    _finish_sync(_empty_result())
+
+    _runner.invoke("start_sync")
+
+    assert_int(_server.count("/sync")).is_equal(1)
+    assert_str(_node("SyncTitleLabel").text).is_equal("Sync Result")