raises regexp

[pytestbot]

Originally reported by: György Kiss (BitBucket: kissgyorgy, GitHub: kissgyorgy)

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I used assertRaisesRegexp in unittest and I miss it from pytest. As I don't want to use unittest anymore :D I wrote a context manager:

#!python

import pytest
import py

class raises_regexp(object):
    def __init__(self, exception, message):
        self.exception = exception
        self.message = message
        self.excinfo = None

    def __enter__(self):
        self.excinfo = object.__new__(py.code.ExceptionInfo)
        return self.excinfo

    def __exit__(self, exc_type, exc_val, exc_tb):
        __tracebackhide__ = True
        if exc_type is None:
            pytest.fail('DID NOT RAISE %s' % self.exception)

        self.excinfo.__init__((exc_type, exc_val, exc_tb))

        if not issubclass(self.excinfo.type, self.exception):
            pytest.fail('%s RAISED instead of %s' % (exc_type, self.exception))

        if self.message not in str(exc_val):
            pytest.fail('message "%s" not found in "%s"' % (self.message, str(exc_val)))

        return True

Usage:

#!python

def test_some_exception_thrown():
    with raises_regexp(ExpectedException, "message contained"):
       # code to test

I think others could benefit from something like this and would be nice to have it in pytest!

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• Bitbucket: https://bitbucket.org/pytest-dev/pytest/issue/372

[pytestbot]

Original comment by György Kiss (BitBucket: kissgyorgy, GitHub: kissgyorgy):

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I made a plugin for this if anyone interested: https://github.com/Walkman/pytest_raisesregexp

[pytestbot]

Original comment by holger krekel (BitBucket: hpk42, GitHub: hpk42):

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What about adding a keyword argument so this would work:

#!python

with pytest.raises(ValueError, regex=r'...'):
      ...

[pytestbot]

Original comment by Ivan Smirnov (BitBucket: aldanor, GitHub: aldanor):

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@walkman_ I'd modify your example code slightly for it to behave more like pytest.raises:

class raises_regexp(object):
    def __init__(self, exception, message, *args, **kwargs):
        self.exception = exception
        self.message = message
        self.excinfo = None
        if args:
            with self:
                args[0](*args[1], **kwargs)

[pytestbot]

Original comment by Ivan Smirnov (BitBucket: aldanor, GitHub: aldanor):

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@hpk42 What do you think about all this? This is one feature that's available in unittest but not available in pytest and it's quite useful.

I think adding a separate function would be cleaner since it would allow you use it same way as pytest.raises without a with block:

pytest.raises_regexp(ValueError, 'expected message', func, 1, 2, a=3, b=4)

Adding a regex keyword argument to pytest.raises wouldn't allow you do use it without a context manager due to ambiguity.

[pytestbot]

Original comment by Floris Bruynooghe (BitBucket: flub, GitHub: flub):

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Would it be very wrong to only support a new regex keyword when used as a context manager? I think the non-context manager only exists because when fist introduced python 2.5 (or earlier) was still supported, but now it should probably be discouraged.

[pytestbot]

Original comment by Bruno Oliveira (BitBucket: nicoddemus, GitHub: nicoddemus):

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I wouldn't mind very much about regex being supported only as a context manager, that's pretty much the only form I use these days...

Anyway, I miss this functionality too and would love to have it built-in, having turned to pytest-raisesregexp in the past. :)

[pytestbot]

Original comment by Ivan Smirnov (BitBucket: aldanor, GitHub: aldanor):

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I use a modified version of this pretty much exclusively without a context manager: less typing required, can use it like a (partial) function, etc :)

[RonnyPfannschmidt]

proposal;

with pytest.raises.matching(ValueError, '.*Regex'):
  ...

[RonnyPfannschmidt]

the builtin solution should modify the context manager and use the regex condition based on the value of the regex attribute

[foxx]

I was almost tempted to use pytest, until I saw this issue :/ Any particular reason why this hasn't been added yet?

[The-Compiler]

Probably a mixture between "nobody has looked at it yet" and "there is a plugin for it" and "it's easy enough to do without pytest support":

with pytest.raises(ValueError) as excinfo:
    func()

assert re.match(pattern, str(excinfo.value))

But since many people have said they'd appreciate such a feature, and nobody seems to have had time yet, I'm sure a contribution would we very welcome!

[nicoddemus]

I could tackle this, but would like to know what is the preferred interface:

1. From pytest-raisesregexp:

   with pytest.raises_regexp(ExpectedException, r".* 1560"):
         function_to_test(arg1)
   
   pytest.raises_regexp(ExpectedException, r".* 1560", function_to_test, arg1):

2. Proposed by @RonnyPfannschmidt:

   with pytest.raises.matching(ValueError, 'regex'):
       function_to_test(arg1)
   
   pytest.raises.matching(ValueError, 'regex', function_to_test, arg1)

3. Any other suggestion? 😄

What do you guys think?

[nicoddemus]

(Just posted a tweet about this).