patch_attribute()

patch_attribute() will, for the duration of the test, change the value of a given attribute:

import math

class ChangePi(TestCase):
  def test_pi(self):
    self.patch_attribute(math, "pi", 4)
    self.assertEqual(math.pi, 4)

patch_attribute() works exclusively with non-callable attributes.

Note

TestSlide provides mock_callable(), mock_async_callable() and mock_constructor() for callables and classes because those require specific functionalities.

You can use patch_attribute() with:

• Modules.

• Classes.

• Instances of classes.

• Class attributes at instances of classes.

• Properties at instances of classes.

Properties are tricky to patch because of the quirky mechanics that Python’s Descriptor Protocol requires. patch_attribute() has support for that so things “just work”:

class WithProperty:
  @property
  def prop(self):
    return "prop"

class PatchingProperties(TestCase):
  def test_property(self):
    with_property = WithProperty()
    self.patch_attribute(with_property, "prop", "mock")
    self.assertEqual(with_property.prop, "mock")

Type Validation

patch_attribute implements type validation and will only allow attributes to be mocked with values of types that match the available typing annotation. TypeCheckerError will be raised if a bad type is given. This check is expected to work 100% of times, but if it does not (possibly a bug in TestSlide, please report!), you can disable it by doing patch_attribute(obj, "attr", "newval", type_validation=False).