Actually, it checks if the dump is the same:

 class ASTTestCase(unittest.TestCase):
    def assertASTEqual(self, ast1, ast2):
        self.assertEqual(ast.dump(ast1), ast.dump(ast2))

    def check_roundtrip(self, code1, filename="internal"):
        ast1 = compile(code1, filename, "exec", ast.PyCF_ONLY_AST)
        unparse_buffer = io.StringIO()
        unparse.Unparser(ast1, unparse_buffer)
        code2 = unparse_buffer.getvalue()
        ast2 = compile(code2, filename, "exec", ast.PyCF_ONLY_AST)
        self.assertASTEqual(ast1, ast2)