Python Mock object with method called multiple times

Solution 1:

Try side_effect

def my_side_effect(*args, **kwargs):
    if args[0] == 42:
        return "Called with 42"
    elif args[0] == 43:
        return "Called with 43"
    elif kwargs['foo'] == 7:
        return "Foo is seven"

mockobj.mockmethod.side_effect = my_side_effect

Solution 2:

A little sweeter:

mockobj.method.side_effect = lambda x: {123: 100, 234: 10000}[x]

or for multiple arguments:

mockobj.method.side_effect = lambda *x: {(123, 234): 100, (234, 345): 10000}[x]

or with a default value:

mockobj.method.side_effect = lambda x: {123: 100, 234: 10000}.get(x, 20000)

or a combination of both:

mockobj.method.side_effect = lambda *x: {(123, 234): 100, (234, 345): 10000}.get(x, 20000)

and merrily on high we go.

Solution 3:

I've ran into this when I was doing my own testing. If you don't care about capturing calls to your methodfromdepclass() but just need it to return something, then the following may suffice:

def makeFakeMethod(mapping={}):
    def fakeMethod(inputParam):
        return mapping[inputParam] if inputParam in mapping else MagicMock()
    return fakeMethod

mapping = {42:"Called with 42", 59:"Called with 59"}
mockobj.methodfromdepclass = makeFakeMethod(mapping)

Here's a parameterized version:

def makeFakeMethod():
    def fakeMethod(param):
        return "Called with " + str(param)
    return fakeMethod

Solution 4:

As in here, apart from using side_effect in unittest.mock.Mock you can also use @mock.patch.object with new_callable, which allows you to patch an attribute of an object with a mock object.

Let's say a module my_module.py uses pandas to read from a database and we would like to test this module by mocking pd.read_sql_table method (which takes table_name as argument).

What you can do is to create (inside your test) a db_mock method that returns different objects depending on the argument provided:

def db_mock(**kwargs):
    if kwargs['table_name'] == 'table_1':
        # return some DataFrame
    elif kwargs['table_name'] == 'table_2':
        # return some other DataFrame

In your test function you then do:

import my_module as my_module_imported

@mock.patch.object(my_module_imported.pd, "read_sql_table", new_callable=lambda: db_mock)
def test_my_module(mock_read_sql_table):
    # You can now test any methods from `my_module`, e.g. `foo` and any call this 
    # method does to `read_sql_table` will be mocked by `db_mock`, e.g.
    ret = my_module_imported.foo(table_name='table_1')
    # `ret` is some DataFrame returned by `db_mock`