Pytest/Hypothesis not matching string as expected

Question

I am testing a validate function I am using with Sanic.

def validate(val):
    try:
        if isinstance(val, bool):  # Here because the int(val) line will success with int(True)/int(False)
            raise ValueError()
        if isinstance(val, float):
            print("IT'S FLOAT!")
            raise ValueError()
        if '.' in str(val):
            raise ValueError()
        n = int(val)
    except ValueError as ex:
        raise InvalidUsage('Invalid value "{}" for int param "n"'.format(val))

I'm testing this against float values and using Hypothesis to generate the test conditions.

@given(val=st.floats())
def test_validate_int_float(val):
    with pytest.raises(InvalidUsage) as ex:
        validate(val)
    print("{}|{}|{}".format(ex.value, f'Invalid value "{val}" for int param "n"',
                            ex.value == f'Invalid value "{val}" for int param "n"'))
    assert ex.match(f'Invalid value "{val}" for int param "n"')

This test fails:

Falsifying example: test_validate_int_float(val=1e+16)

The print statement looks like this:

IT'S FLOAT!
Invalid value "1e+16" for int param "n"|Invalid value "1e+16" for int param "n"|False

Why is my assert not matching? The strings look the same to me. I am assuming it's due to the float value, but in that case, how do I properly match the value?

ipaleka · Accepted Answer · 2019-10-15T20:08:30.990

1

Convert the ex.value to str prior to checking equality with:

print("{}|{}|{}".format(ex.value, f'Invalid value "{val}" for int param "n"',
                        str(ex.value) == f'Invalid value "{val}" for int param "n"'))

edited Oct 15 '19 at 20:08

answered Oct 15 '19 at 18:09

ipaleka

3,745
2
13
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Thanks for the information about `str()`. However, I don't think the comment about not hitting the ValueError is correct. I've updated my post to show the print statement I added in (without the `str()` fix to keep your answer valid). It's printing the statement as expected. – NewGuy Oct 15 '19 at 19:40
Yep, I was wrong about that part and edited my answer. – ipaleka Oct 15 '19 at 20:10

score 0 · Answer 2 · answered Oct 16 '19 at 12:13

0

What version of pytest and of Python? I'm pretty sure this is a pytest usage issue, not anything to do with Hypothesis.

While not an answer, using the match argument to pytest.raises rather than the method on the thing it returns is often easier to read, and I suspect would not have the same issue.

answered Oct 16 '19 at 12:13

Zac Hatfield-Dodds

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6
19

Hypothesis - 4.36.2, Pytest - 5.1.3 – NewGuy Oct 16 '19 at 18:07

Pytest/Hypothesis not matching string as expected

2 Answers2