How to mock patch a python class and get a new Mock object for each instantiation?

How to mock patch a python class and get a new Mock object for each instantiation?

To mock patch a Python class and get a new Mock object for each instantiation, you can use the patch decorator or context manager provided by the unittest.mock library. You can set the return value of the mocked class to a new Mock object for each instantiation. Here's how to do it:

Let's assume you have a class MyClass that you want to mock, and you want a new Mock object returned for each instance:

from unittest.mock import patch, Mock

class MyClass:
    def __init__(self):
        self.data = "real data"

# Function that creates instances of MyClass
def create_instances():
    instance1 = MyClass()
    instance2 = MyClass()
    return instance1, instance2

Now, you can write a test case using patch to mock MyClass and return a new Mock object for each instantiation:

import unittest
from unittest.mock import patch

class TestMyClass(unittest.TestCase):

    @patch('__main__.MyClass', side_effect=lambda: Mock())
    def test_create_instances(self, mock_myclass):
        instance1, instance2 = create_instances()

        # Check that instance1 and instance2 are Mock objects
        self.assertIsInstance(instance1, Mock)
        self.assertIsInstance(instance2, Mock)

        # Check that they are different objects
        self.assertIsNot(instance1, instance2)

if __name__ == '__main__':
    unittest.main()

In this example:

  • We use the @patch decorator to mock the MyClass class. The side_effect parameter is a lambda function that returns a new Mock object for each instantiation of MyClass.

  • In the test_create_instances method, we call create_instances, which creates two instances of MyClass. Both instances are now mocked with Mock objects.

  • We use self.assertIsInstance to check that both instance1 and instance2 are instances of Mock.

  • Finally, we use self.assertIsNot to ensure that instance1 and instance2 are different objects, meaning that each instantiation of MyClass returns a new Mock object.

This way, you can mock MyClass and ensure that you get a new Mock object for each instantiation during your tests.

Examples

  1. "Mock patching a Python class instantiation example"

    Description: This search query is aimed at finding an example demonstrating how to use the unittest.mock.patch module in Python to mock the instantiation of a class and obtain a new Mock object for each instantiation.

    import unittest
from unittest.mock import patch

class MyClass:
    def __init__(self):
        pass

    def method(self):
        pass

class TestMyClass(unittest.TestCase):
    @patch('path.to.your.module.MyClass', autospec=True)
    def test_mock_class_instantiation(self, MockMyClass):
        instance1 = MockMyClass()
        instance2 = MockMyClass()

        self.assertIsNot(instance1, instance2)
        self.assertTrue(isinstance(instance1, MyClass))
        self.assertTrue(isinstance(instance2, MyClass))

    This code demonstrates how to use patch to mock the instantiation of MyClass. The autospec=True parameter ensures that the mock has the same attributes and methods as the class being mocked.

  2. "Python unittest.mock.patch class instantiation with side effects"

    Description: This query seeks information on how to use unittest.mock.patch with side effects to control the behavior of the mocked class during instantiation.

    from unittest.mock import patch

class MyClass:
    def __init__(self):
        self.value = 10

with patch('path.to.your.module.MyClass') as MockMyClass:
    MockMyClass.return_value.value = 20
    instance = MyClass()

print(instance.value)  # Output: 20

    In this code, patch is used as a context manager to mock the instantiation of MyClass. The return_value attribute of the mock is used to set the value of an attribute (value in this case) during instantiation.

  3. "Python mock.patch class constructor parameters"

    Description: This query is about how to mock a class constructor in Python using mock.patch and provide custom parameters during instantiation.

    from unittest.mock import patch

class MyClass:
    def __init__(self, param):
        self.param = param

with patch('path.to.your.module.MyClass') as MockMyClass:
    MockMyClass.return_value.param = "custom_value"
    instance = MyClass("original_value")

print(instance.param)  # Output: "custom_value"

    Here, the param attribute of the mocked class instance is set to "custom_value", overriding the parameter passed during instantiation.

  4. "Python unittest.mock.patch multiple class instantiations"

    Description: This query is looking for information on how to mock multiple instantiations of a class using unittest.mock.patch.

    from unittest.mock import patch

class MyClass:
    def __init__(self):
        pass

with patch('path.to.your.module.MyClass') as MockMyClass:
    instance1 = MockMyClass()
    instance2 = MockMyClass()

# Additional assertions or operations on instance1 and instance2

    In this code, patch is used to mock the class MyClass and then two instances of the mocked class are created. This demonstrates mocking multiple instantiations of a class.

  5. "Python mock.patch with multiple class mocks"

    Description: This query is about using mock.patch with multiple classes for mocking in Python.

    from unittest.mock import patch

class ClassA:
    pass

class ClassB:
    pass

with patch('path.to.your.module.ClassA') as MockClassA, \
     patch('path.to.your.module.ClassB') as MockClassB:
    instance_a = MockClassA()
    instance_b = MockClassB()

# Additional assertions or operations on instance_a and instance_b

    This code demonstrates how to use patch with multiple classes (ClassA and ClassB), each mocked within its respective context manager.

  6. "Python mock.patch class method calls"

    Description: This query is aimed at understanding how to use mock.patch to mock method calls of a class in Python.

    from unittest.mock import patch

class MyClass:
    def method(self):
        return "original_method"

with patch('path.to.your.module.MyClass') as MockMyClass:
    MockMyClass().method.return_value = "mocked_method"
    instance = MyClass()

print(instance.method())  # Output: "mocked_method"

    Here, the method of the mocked MyClass instance is replaced with a custom return value, demonstrating how to mock method calls.

  7. "Python mock.patch class instantiation with return value"

    Description: This query seeks information on how to use mock.patch to control the return value of a class instantiation in Python.

    from unittest.mock import patch

class MyClass:
    def __init__(self):
        pass

with patch('path.to.your.module.MyClass') as MockMyClass:
    MockMyClass.return_value = "mocked_instance"
    instance = MyClass()

print(instance)  # Output: "mocked_instance"

    In this code, the return value of the mocked MyClass instance is set to "mocked_instance".

  8. "Python unittest.mock.patch object attributes"

    Description: This query is about how to use unittest.mock.patch to manipulate object attributes during class instantiation.

    from unittest.mock import patch

class MyClass:
    def __init__(self):
        self.value = "original_value"

with patch('path.to.your.module.MyClass') as MockMyClass:
    MockMyClass.return_value.value = "mocked_value"
    instance = MyClass()

print(instance.value)  # Output: "mocked_value"

    Here, the value attribute of the mocked MyClass instance is set to "mocked_value".

  9. "Python unittest.mock.patch instance count"

    Description: This query aims to understand how to count the number of times a class is instantiated using unittest.mock.patch.

    from unittest.mock import patch

class MyClass:
    def __init__(self):
        pass

with patch('path.to.your.module.MyClass') as MockMyClass:
    instance1 = MockMyClass()
    instance2 = MockMyClass()

    assert MockMyClass.call_count == 2

    In this code, call_count attribute of the mock is used to check how many times the class MyClass was instantiated.

  10. "Python unittest.mock.patch class inheritance"

    Description: This query focuses on how to use unittest.mock.patch with class inheritance in Python.

    from unittest.mock import patch

class BaseClass:
    def method(self):
        return "base_method"

class SubClass(BaseClass):
    pass

with patch('path.to.your.module.BaseClass') as MockBaseClass:
    MockBaseClass.return_value.method.return_value = "mocked_method"
    instance = SubClass()

print(instance.method())  # Output: "mocked_method"

    In this code, unittest.mock.patch is used to mock the method of the base class (BaseClass) even when it is called from a subclass (SubClass).

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