How to mock a function directly (Python)

Question

We create mock objects and specify the behavior of methods called on them:

from unittest.mock import patch, Mock

execute = Mock()
execute.fetchone = Mock(return_value={'state': json.dumps({})})
with patch('modules.data_chat.chatbot.execute', new=lambda x, y, z: execute):
        auto_reply(None, "test_user_id", "Hello?", 1)

assert execute.fetchone.called
assert execute.called

code under test (auto_reply) implementation:

from tools.db_tools import execute
[...]
cur = execute(conn, sql, (bot_id, channel_id))
state = cur.fetchone()

Back in the test code, execute.fetchone.called == True. However, execute.called == False

Why is execute.called == False and how can I fix this? Is new=lambda x, y, z: execute correct?

Daniel Roseman · Accepted Answer · 2019-05-06 11:31:39Z

3

Because you didn't call it. You called a lambda, which returned it.

I'm not sure why you are doing this. You should use the mocks.

fetchone = Mock(return_value={'state': json.dumps({})})
execute = Mock(return_value=fetchone)
with patch('modules.data_chat.chatbot.execute', new=execute):
    ...

answered May 6, 2019 at 11:31

Daniel Roseman

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1 Comment

chepner Over a year ago

This also corrects the error of treating fetchone as an attribute of execute, rather than an attribute of the return value of execute.

Nino van Hooff · Accepted Answer · 2019-05-08 08:49:02Z

0

@Daniel Roseman put me on the right track. One step in the chain was missing in his answer though. execute should not return fetchone directly, but a cursor mock; which can mock fetchone. I added names to the mocks for debugging purposes:

cursorMock = Mock(name="cursorMock")
cursorMock.fetchone = Mock(name="fetchoneMock", return_value={'state': json.dumps({})})

execute = Mock(name="executeMock", return_value=cursorMock)
with patch('modules.data_chat.chatbot.execute', new=execute):
    ...

assert cursorMock.fetchone.called
assert execute.called

edited May 8, 2019 at 8:49

answered May 8, 2019 at 8:39

Nino van Hooff

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