The Mock Object

Defining a Mock Object

Take a close look at this code.

Try to predict what will happen.

from unittest.mock import Mock
mock = Mock()
mock.return_value = 3
mock()
mock.assert_called_once_with()
mock()
mock.assert_called_once_with()

Let’s read this code together now:

• In the line mock = Mock(), we are instantiating the mock object.

• In the line mock.return_value = 3, we are assigning a return value for this instance of the object. That means that every time I call mock() (the instance of Mock()), I’ll get a value of 3.

• Look at mock.assert_called_once_with(). Here we are asserting that we called the method with no parameters once. An AssertionError will be raised if this assertion fails. This happens on the second time we call mock.assert_called_once_with().

Now you’ve just learned to assert mocked method calls

Mapping method to be mocked by Mock

In development

Mapping exceptions

In development

More on side-effect

In development

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