[Python] Correct usage of assertRaises in Python unit tests

I'm trying to figure out how to correctly use assertRaises() of the Python unittest module. I have a ValueError in my function that gets raised. However, when testing in my unit tests, I'm getting mixed results with two different ways of using assertRaises().

When I write the test like this, it works:

import unittest

class MyTest(unittest.TestCase):

@classmethod
def setUpClass(cls):
pass

def test_error(self):
with self.assertRaises(ValueError):
func(a)


However, if I write my test like below, it does not work even though the ValueError gets raised:

def test_error(self):
self.assertRaises(ValueError, func(a))


Why would one way work and not the other?

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