How to use pytest to check that Error is NOT raised Ask Question

How to use pytest to check that Error is NOT raised Ask Question

Let's assume we have smth like that :

import py, pytest

ERROR1 = ' --- Error : value < 5! ---'
ERROR2 = ' --- Error : value > 10! ---'

class MyError(Exception):
    def __init__(self, m):
        self.m = m

    def __str__(self):
        return self.m

def foo(i):
    if i < 5:
        raise MyError(ERROR1)
    elif i > 10:
        raise MyError(ERROR2)
    return i


# ---------------------- TESTS -------------------------
def test_foo1():
    with pytest.raises(MyError) as e:
        foo(3)
    assert ERROR1 in str(e)

def test_foo2():
    with pytest.raises(MyError) as e:
        foo(11)
    assert ERROR2 in str(e)

def test_foo3():
        ....
        foo(7)
         ....

Q: How can I make test_foo3() to test, that no MyError is raised? It's obvious, that i could just test :

def test_foo3():
    assert foo(7) == 7

but i want to test that via pytest.raises(). Is is possible someway? For example: in a case, that function "foo" has no return-value at all,

def foo(i):
    if i < 5:
        raise MyError(ERROR1)
    elif i > 10:
        raise MyError(ERROR2)

it could make sense to test this way, imho.

ベストアンサー1

A test will fail if it raises any kind of unexpected Exception. You can just invoke foo(7) and you will have tested that no MyError is raised. So, following will suffice:

def test_foo3():
    foo(7)

If you want to be explicit and write an assert statement for this, you can do:

def test_foo3():
    try:
        foo(7)
    except MyError:
        pytest.fail("Unexpected MyError ..")

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