How to use the executing.TESTING function in executing

import ast
import inspect
import executing

executing.TESTING = 1

from executing import Source


class Tester(object):
    def get_node(self, typ):
        frame = inspect.currentframe().f_back.f_back
        Source.lazycache(frame)
        node = Source.executing(frame).node
        assert isinstance(node, typ), (node, typ)
        return node

    def check(self, node, value):
        frame = inspect.currentframe().f_back.f_back
        result = eval(
            compile(ast.Expression(node), frame.f_code.co_filename, 'eval'),