chore: add GUT test framework

addons/gut/scratch/demo_signal_parameter_error.gd

@@ -0,0 +1,13 @@
+extends SceneTree
+
+signal the_signal(one)
+
+func signal_callback(one):
+    print(one)
+
+func _init():
+    var callback = signal_callback.bind("two")
+    the_signal.connect(callback)
+    the_signal.emit('foo')
+
+    quit()