python - How to mock nested functions?

Question

The mocking library I use is ... mock.

I came across this "mock nested functions" problem when I tried to write test case for a function(legacy code).

This function used a very complex nested function with heavy dependencies on other modules.

I wonder if it's possible to mock nested functions with mock.

Answer 1

for example you need to mock nested function calls (chained functions) from Google DRIVE API

result = get_drive_service().files().insert(body='body', convert=True).execute()   

so you need to patch through functions: service_mock(), files(), insert(), till last execute() response:

from mock import patch
with patch('path.to.import.get_drive_service') as service_mock:
   service_mock.return_value.files.return_value.insert.
   return_value.execute.return_value = {'key': 'value', 'status': 200}

Main scheme: first.return_value.second.return_value.third.return_value.last.return_value = rsp