assertRaises only catch base Exception in unittest

Question

I work on PyCharm, here is my project structure :

Python
|   utils
|   |  __init__.py
|   |  test_utils.py
|   main.py

In utils/__init__.py :

# -*- coding : utf-8 -*-
"""
Created on 15/10/2020

"""

import random

import datetime


def random_value(min_x, max_x):
    # Verification of the type of parameters
    try:
        assert(type(min_x) is type(max_x))
    except AssertionError:
        raise TypeError('Limits for x must be of the same type')

    # Verification of the inferiority of min_x in front of max_x
    try:
        assert(min_x < max_x)
    except AssertionError:
        raise ValueError('min_x has to be lower than max_x')

    # Definition of result
    x = None

    # If we want float
    if isinstance(min_x, float):
        x = random.uniform(min_x, max_x)

    # If we want int
    elif isinstance(min_x, int):
        x = random.randint(min_x, max_x)

    # If we want datetime.datetime
    elif isinstance(min_x, datetime.datetime):
        x = min_x + datetime.timedelta(seconds=random.randint(0, int((max_x - min_x).total_seconds())), )

    # In other cases, raise of exception
    else:
        raise TypeError('min_x and max_x type is not compatible with function')
    return x

In utils/test_utils.py

import unittest
import utils
import datetime


class UtilsTest(unittest.TestCase):
    def test_random_value(self):
        self.assertRaises(TypeError, utils.random_value, 2.0, 3)

        self.assertAlmostEqual(utils.random_value(1.0, 1.5), 1.25, delta=0.25)
        self.assertIn(utils.random_value(1, 3), [1, 2, 3])

        start = datetime.datetime(1998, 5, 5)
        end = datetime.datetime(1998, 5, 10)
        x = utils.random_value(start, end)
        self.assertIsInstance(x, datetime.datetime)
        self.assertTrue((start <= x) and (x <= end))


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

When I run utils/test_utils.py to test utils/__init__.py, I have this error concerning the first self.assertRaises(TypeError, utils.random_value, 2.0, 3) :

Testing started at 10:23 ...
Python/utils/test_utils.py"
Launching unittests with arguments python -m unittest Python/utils/test_utils.py in Python\utils



Ran 1 test in 0.009s

FAILED (errors=1)

Error
Traceback (most recent call last):
  File "Python\utils\__init__.py", line 18, in random_value
    assert(type(min_x) is type(max_x))
AssertionError

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "Python\lib\unittest\case.py", line 60, in testPartExecutor
    yield
  File "Python\lib\unittest\case.py", line 676, in run
    self._callTestMethod(testMethod)
  File "Python\lib\unittest\case.py", line 633, in _callTestMethod
    method()
  File "Python\utils\test_utils.py", line 8, in test_random_value
    self.assertRaises(AssertionError, utils.random_value, 2.0, 3)
  File "Python\lib\unittest\case.py", line 816, in assertRaises
    return context.handle('assertRaises', args, kwargs)
  File "Python\lib\unittest\case.py", line 202, in handle
    callable_obj(*args, **kwargs)
  File "Python\utils\__init__.py", line 20, in random_value
    raise TypeError('Limits for x must be of the same type')
TypeError: Limits for x must be of the same type


Process finished with exit code 1

Assertion failed

Assertion failed

Assertion failed

Assertion failed

Assertion failed

Assertion failed

But when I use self.assertRaises(Exception, utils.random_value, 2.0, 3), it works... (and it's not working with AssertionError).

Why assertRaises only catch base Exception?

Answer 1

I found a solution : assertRaises((AssertionError, TypeError), utils.random_value, 2.0, 3)

But @jonrsharpe gave me a better advice :

In utils/__init__.py:

Replace the structure :

try:
   assert(type(min_x) is type(max_x))
except AssertionError:
   raise TypeError

by:

if not (type(min_x) is type(max_x)):
   raise TypeError

And so the command assertRaises(TypeError, utils.random_value, 2.0, 3) works in utils/test_utils.py.