[Pytest-commit] Issue #580: OutcomeException should not be a subclass of Exception (hpk42/pytest)

[thiefmaster]

New issue 580: OutcomeException should not be a subclass of Exception
https://bitbucket.org/hpk42/pytest/issue/580/outcomeexception-should-not-be-a-subclass

thiefmaster:

Imagine this code:

```
def blackbox(callback, arg):
    # this is assumed to be application code
    try:
        callback(arg)
    except Exception:
        pass


def test_callback():
    def cb(x):
        if not x:
            import pytest
            pytest.fail('foo')

    blackbox(cb, True)
    blackbox(cb, False)
```

The testcase will pass since `except Exception` will catch the `Failed` raised by `pytest.fail`. However, I don't think there is *any* valid use-case for application code to prevent a testcase failure from propagating to the test runner.

A more practical example where this is a major issue is monkeypatching a library function to fail when called. For example, one might want to monkeypatch `smtplib.SMTP.connect` to fail when code tries to send an email unexpectedly - but chances are good that the application is wrapping that code in a `try...except Exception` block to prevent an email sending failure from breaking things (e.g. because the email is not very important). So now the `pytest.fail` called in the monkeypatched method will never propagate since it's caught by application code.