Required import is not added when functions returns class from a library

[tyuldashev]

Description

When UTBot generates tests for methods which return class from the library it doesn't add import statement to test file, so such test always fails.

To Reproduce

Steps to reproduce the behavior:

import json


def some_json():
    return json.JSONDecoder

1. Use code above to reproduce the problem
2. Generate test for that code
3. Run generated tests

Expected behavior

Generated test runs without issues

Actual behavior

Generated test fails because import of json is not added to test file.

Visual proofs (screenshots, logs, images)

[tyuldashev]

There is also problem with import when method returns function. Let me know if dedicated case is required.

Code under test

def return_lambda(n):
    return lambda x: x*n

Failing part of generated test

...
self.assertTrue(isinstance(actual, builtins.function))
...

[tyuldashev]

Unfortunately cannot reverify issue, because now UTBot doesn't generate tests for functions without parameters.

Also problem with builtins.functions from the comment still reproducible.