Using mock to test if directory exists or not

I have been exploring mock and pytest for a few days now.

I have the following method:

def func():
    if not os.path.isdir('/tmp/folder'):
        os.makedirs('/tmp/folder')

In order to unit test it, I have decided to patch os.path.isdir and os.makedirs, as shown:

@patch('os.path.isdir')
@patch('os.makedirs')
def test_func(patch_makedirs, patch_isdir):
    patch_isdir.return_value = False
    assert patch_makedirs.called == True

The assertion fails, irrespective of the return value from patch_isdir. Can someone please help me figure out where I am going wrong?