Check if expection is raised with pytest

Question

Being quite new to exception test handling I am wondering how to check if an assertion is raised.

a.py

class SomeError(Exception):
    pass

class SomeClass(object):
    def __init__(self):
        ...
        raise SomeError
        ...

test_a.py

from a.a import SomeClass

def test_some_exception_raised():
    ?

What assertion should it be there to check if SomeError is raised? I am using pytest.

Akshay Pratap Singh · Accepted Answer · 2021-05-04T11:47:36.527

8

In order to write assertions about raised exceptions, you can use pytest.raises as a context manager like this:

a.py

class SomeError(Exception):
    pass

class SomeClass(object):
    def __init__(self):
        ...
        raise SomeError("some error message")
        ...

test_a.py

from .a import SomeClass, SomeError
import pytest

def test_some_exception_raised():
    with pytest.raises(SomeError) as excinfo:   
        obj = SomeClass()  
    
    assert 'some error message' in str(excinfo.value)

For more about exception assertions, see here

edited May 04 '21 at 11:47

answered Mar 28 '17 at 13:41

Akshay Pratap Singh

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Thanks! So when I raise the exception I have to add some parameter, i.e., `raise SomeError('some error message')`? – Mihai Mar 28 '17 at 14:05
@Mihai see now answer to understand. – Akshay Pratap Singh Mar 28 '17 at 14:09
Do you know why PyCharm attentions me like this: Expected type 'TypeVar('T')', got 'Type[SomeError]' instead? – Mihai Mar 31 '17 at 07:07
2

Shouldn't the `assert` be outside the `with` block? – simanacci Aug 24 '20 at 12:44
@simanacci is correct, `assert` should be in line with the `with` block, not inside it (silly Python and your indentation) – Kevin May 03 '21 at 18:44

Check if expection is raised with pytest

1 Answers1