Python mock multiple return values

I am using pythons mock.patch and would like to change the return value for each call.
Here is the caveat:
the function being patched has no inputs, so I can not change the return value based on the input.

Here is my code for reference.

def get_boolean_response():
    response = io.prompt('y/n').lower()
    while response not in ('y', 'n', 'yes', 'no'):
        io.echo('Not a valid input. Try again'])
        response = io.prompt('y/n').lower()

    return response in ('y', 'yes')

My Test code:

@mock.patch('io')
def test_get_boolean_response(self, mock_io):
    #setup
    mock_io.prompt.return_value = ['x','y']
    result = operations.get_boolean_response()

    #test
    self.assertTrue(result)
    self.assertEqual(mock_io.prompt.call_count, 2)

io.prompt is just a platform independent (python 2 and 3) version of “input”. So ultimately I am trying to mock out the users input. I have tried using a list for the return value, but that doesn’t seam to work.

You can see that if the return value is something invalid, I will just get an infinite loop here. So I need a way to eventually change the return value, so that my test actually finishes.

(another possible way to answer this question could be to explain how I could mimic user input in a unit-test)

Not a dup of this question mainly because I do not have the ability to vary the inputs.

One of the comments of the Answer on this question is along the same lines, but no answer/comment has been provided.

Answers:

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Method 1

You can assign an iterable to side_effect, and the mock will return the next value in the sequence each time it is called:

>>> from unittest.mock import Mock
>>> m = Mock()
>>> m.side_effect = ['foo', 'bar', 'baz']
>>> m()
'foo'
>>> m()
'bar'
>>> m()
'baz'

Quoting the Mock() documentation:

If side_effect is an iterable then each call to the mock will return the next value from the iterable.

Method 2

for multiple return values, we can use side_effect during patch initializing also and pass iterable to it

sample.py

def hello_world():
    pass

test_sample.py

from unittest.mock import patch
from sample import hello_world

@patch('sample.hello_world', side_effect=[{'a': 1, 'b': 2}, {'a': 4, 'b': 5}])
def test_first_test(self, hello_world_patched):
    assert hello_world() == {'a': 1, 'b': 2}
    assert hello_world() == {'a': 4, 'b': 5}
    assert hello_world_patched.call_count == 2

Method 3

You can also use patch for multiple return values:

@patch('Function_to_be_patched', return_value=['a', 'b', 'c'])

Remember that if you are making use of more than one patch for a method then the order of it will look like this:

@patch('a')
@patch('b')
def test(mock_b, mock_a);
    pass

as you can see here, it will be reverted. First mentioned patch will be in the last position.

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0