chore: add GUT test framework

addons/gut/scratch/demo_extends_issue.gd

@@ -0,0 +1,66 @@
+# Script to demo this failing test:
+#
+# func test_doubled_instances_extend_the_inner_class():
+# 	var inst = doubler.double_inner(INNER_CLASSES_PATH, 'InnerA').new()
+# 	assert_is(inst, InnerClasses.InnerA)
+extends SceneTree
+
+const INNER_CLASSES_PATH = 'res://test/resources/doubler_test_objects/inner_classes.gd'
+var InnerClasses = load(INNER_CLASSES_PATH)
+
+class ExtendsInnerClassesInnerAWithPath:
+	extends 'res://test/resources/doubler_test_objects/inner_classes.gd'.InnerA
+
+func make_script(script_source):
+	var DynScript = GDScript.new()
+	DynScript.source_code = script_source
+	DynScript.reload()
+	return DynScript
+
+
+# this works
+func demo_node2d():
+	var script_source = '' + \
+	"extends Node2D\n" + \
+	"func hello_world():\n" + \
+	"\tprint('--- hello world ---')"
+
+	print(script_source)
+
+	var inst = make_script(script_source).new()
+	if(inst is Node2D):
+		print('pass - yes it is')
+	else:
+		print('fail - unfortunately it is not')
+
+	inst.free()
+
+
+func demo_dyn_inner_class():
+	print('-- demo_dyn_inner_class')
+	var script_source = '' + \
+	"extends '" + INNER_CLASSES_PATH + "'.InnerA\n"
+	var inst = make_script(script_source).new()
+
+	if(inst is InnerClasses):
+		print('fail - is InnerClasses')
+	if(inst is InnerClasses.InnerA):
+		print('pass - is InnerA')
+
+
+func demo_inner_extends_full_path():
+	print('-- demo_inner_extends_full_path')
+	var inst = ExtendsInnerClassesInnerAWithPath.new()
+	print(inst.get_a())
+	if(inst is InnerClasses):
+		print('fail - 2 is InnerClasses')
+	if(inst is InnerClasses.InnerA):
+		print('pass - 2 is InnerA')
+
+
+# Currently not demoing anything wrong.
+func _init():
+	demo_dyn_inner_class()
+	demo_inner_extends_full_path()
+	demo_node2d()
+	quit()