How to replace variable inside function in unittest- pytest

Question

I have a problem with replace variable inside method which i have to test, namely:

def find_files(path):
    path_dir = os.listdir(path)
    ...

and for needs of test I have to replace path_dir from real result of os.listdir to some test list i.e. ['whatever1.txt', 'whatever2.txt', 'whatever3.txt']

How to do it? BR, Damian

You may want to look into the patch functionality of pytest-mock. — das-g
– das-g, Commented May 9, 2018 at 12:32

Radostin Stoyanov · Accepted Answer · 2018-05-09 13:12:43Z

4

You can use mock.patch to set return value for your variable. For example

with patch('os.listdir') as mocked_listdir:
    mocked_listdir().return_value = ['.', '..']
    find_files(path)

or alternatively you can set a side effect

with patch('os.listdir') as mocked_listdir:
    mocked_listdir().side_effect = some_other_function
    find_files(path)

answered May 9, 2018 at 13:12

Radostin Stoyanov

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2 Comments

Damian Silkowski Over a year ago

Thanks, I had a kind of eclipse of the mind because i know it, and I used it. Doesn't matter. Thanks for your help :)

Simplecode Over a year ago

How to mock if I have a list comprehension assigned as variable ? Eg ``` def xyx(): x = [s for i in list_example if i >0] # I want to mock this expression. ```

Sriram · Accepted Answer · 2018-05-09 12:32:08Z

-1

You should try mock os.listdir to return the mock test data.

answered May 9, 2018 at 12:32

Sriram

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2 Comments

Damian Silkowski Over a year ago

Ok I can mock os.listdir but i need to variable path_dir.

Sriram Over a year ago

If you mock it with the result you need to return, it will return that when it is called so it will be automatically stored to path_dir

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