assert_called
- Python course
- Advanced
- Lesson 23/83
- 5 min
Learn call verification with assert_called_with.
assert_called
To check whether a Mock was called, use the assert_called family. The most basic is assert_called(): it passes silently if called at least once; it raises AssertionError if not called.
Stricter checks: assert_called_once() exactly once; assert_called_with(arg) with specific arguments; assert_called_once_with(arg) exactly once and with specific arguments.
m = Mock()
m(5)
m.assert_called_with(5) # passes
m.assert_called_with(6) # raisesThese checks verify that the mocked function was called with the right arguments; they inspect fake-object behavior at the end of the test.
Call arguments and order
You can read a Mock's call history with call_args_list. Each entry is a tuple holding the positional and keyword arguments of one call.
This is handy to check call order and the arguments of each call. If a function was called first with (5,) then with (6,), call_args_list lists both.
This helps in multi-call scenarios where simple assert_called_with is not enough.
Practice Check with assert_called_with
Import Mock from unittest.mock. Create m = Mock(); call m("Ayşe"). Add the check m.assert_called_with("Ayşe"). Finally print print("ok").
Starter code
# import Mock from unittest.mock
# create Mock m; call with "Ayşe"
# check with assert_called_with("Ayşe")
# print "ok"Sample solution
from unittest.mock import Mock
m = Mock()
m("Ayşe")
m.assert_called_with("Ayşe")
print("ok")Expected output
ok
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Match the assertion methods
| Term | Meaning |
|---|---|
assert_called() |
At least once |
assert_called_once() |
Exactly once |
assert_called_with(x) |
With specific arg |
assert_called_once_with(x) |
Exactly once with specific |
2 When does assert_called_once() raise?
- If the Mock was never called
- If the Mock was called more than once
- Both if never called and if called more than once Correct answer
- If the Mock was called once
Explanation: assert_called_once() expects exactly one call; otherwise it raises.
3 assert_called_with call
from unittest.mock import Mock
m = Mock()
m(5)
m.____(5)from unittest.mock import Mock
m = Mock()
m(5)
m.assert_called_with(5)Explanation: m.assert_called_with(5) checks the Mock was called with 5.