Fix UnicodeEncodeError when string comparison with unicode has failed.

[AiOO]

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UnicodeEncodeError is occurred when comparing two strings with any unicode character. This PR fixes this error.

Relative issue: #1864.

Error reproduction:

$ cat test.py
# -*- coding: utf-8 -*-
def test_with_unicode_literal():
    assert u'테스트' == u'Test'

$ py.test test.py
==================================================== test session starts =====================================================
platform darwin -- Python 2.7.12, pytest-3.0.0, py-1.4.31, pluggy-0.3.1
rootdir: /Users/bright/Playground/test_test, inifile:
collected 1 items
test.py
INTERNALERROR> Traceback (most recent call last):
INTERNALERROR>   File "/REDUCED/lib/python2.7/site-packages/_pytest/main.py", line 96, in wrap_session
INTERNALERROR>     session.exitstatus = doit(config, session) or 0
INTERNALERROR>   File "/REDUCED/lib/python2.7/site-packages/_pytest/main.py", line 131, in _main
INTERNALERROR>     config.hook.pytest_runtestloop(session=session)
INTERNALERROR>   File "/REDUCED/lib/python2.7/site-packages/_pytest/vendored_packages/pluggy.py", line 724, in __call__
INTERNALERROR>     return self._hookexec(self, self._nonwrappers + self._wrappers, kwargs)
INTERNALERROR>   File "/REDUCED/lib/python2.7/site-packages/_pytest/vendored_packages/pluggy.py", line 338, in _hookexec
INTERNALERROR>     return self._inner_hookexec(hook, methods, kwargs)
INTERNALERROR>   File "/REDUCED/lib/python2.7/site-packages/_pytest/vendored_packages/pluggy.py", line 333, in <lambda>
INTERNALERROR>     _MultiCall(methods, kwargs, hook.spec_opts).execute()
INTERNALERROR>   File "/REDUCED/lib/python2.7/site-packages/_pytest/vendored_packages/pluggy.py", line 596, in execute
INTERNALERROR>     res = hook_impl.function(*args)
INTERNALERROR>   File "/REDUCED/lib/python2.7/site-packages/_pytest/main.py", line 152, in pytest_runtestloop
INTERNALERROR>     item.config.hook.pytest_runtest_protocol(item=item, nextitem=nextitem)
INTERNALERROR>   File "/REDUCED/lib/python2.7/site-packages/_pytest/vendored_packages/pluggy.py", line 724, in __call__
INTERNALERROR>     return self._hookexec(self, self._nonwrappers + self._wrappers, kwargs)
INTERNALERROR>   File "/REDUCED/lib/python2.7/site-packages/_pytest/vendored_packages/pluggy.py", line 338, in _hookexec
INTERNALERROR>     return self._inner_hookexec(hook, methods, kwargs)
INTERNALERROR>   File "/REDUCED/lib/python2.7/site-packages/_pytest/vendored_packages/pluggy.py", line 333, in <lambda>
INTERNALERROR>     _MultiCall(methods, kwargs, hook.spec_opts).execute()
INTERNALERROR>   File "/REDUCED/lib/python2.7/site-packages/_pytest/vendored_packages/pluggy.py", line 595, in execute
INTERNALERROR>     return _wrapped_call(hook_impl.function(*args), self.execute)
INTERNALERROR>   File "/REDUCED/lib/python2.7/site-packages/_pytest/vendored_packages/pluggy.py", line 253, in _wrapped_call
INTERNALERROR>     return call_outcome.get_result()
INTERNALERROR>   File "/REDUCED/lib/python2.7/site-packages/_pytest/vendored_packages/pluggy.py", line 279, in get_result
INTERNALERROR>     _reraise(*ex)  # noqa
INTERNALERROR>   File "/REDUCED/lib/python2.7/site-packages/_pytest/vendored_packages/pluggy.py", line 264, in __init__
INTERNALERROR>     self.result = func()
INTERNALERROR>   File "/REDUCED/lib/python2.7/site-packages/_pytest/vendored_packages/pluggy.py", line 596, in execute
INTERNALERROR>     res = hook_impl.function(*args)
INTERNALERROR>   File "/REDUCED/lib/python2.7/site-packages/_pytest/runner.py", line 66, in pytest_runtest_protocol
INTERNALERROR>     runtestprotocol(item, nextitem=nextitem)
INTERNALERROR>   File "/REDUCED/lib/python2.7/site-packages/_pytest/runner.py", line 79, in runtestprotocol
INTERNALERROR>     reports.append(call_and_report(item, "call", log))
INTERNALERROR>   File "/REDUCED/lib/python2.7/site-packages/_pytest/runner.py", line 133, in call_and_report
INTERNALERROR>     call = call_runtest_hook(item, when, **kwds)
INTERNALERROR>   File "/REDUCED/lib/python2.7/site-packages/_pytest/runner.py", line 151, in call_runtest_hook
INTERNALERROR>     return CallInfo(lambda: ihook(item=item, **kwds), when=when)
INTERNALERROR>   File "/REDUCED/lib/python2.7/site-packages/_pytest/runner.py", line 168, in __init__
INTERNALERROR>     self.excinfo = ExceptionInfo()
INTERNALERROR>   File "/REDUCED/lib/python2.7/site-packages/_pytest/_code/code.py", line 357, in __init__
INTERNALERROR>     exprinfo = str(tup[1])
INTERNALERROR> UnicodeEncodeError: 'ascii' codec can't encode characters in position 8-10: ordinal not in range(128)
================================================ no tests ran in 0.01 seconds ================================================

[coveralls]

Coverage decreased (-0.02%) to 93.006% when pulling 6cbcc35 on AiOO:bugfix/assertion-with-unicode into 9c45d6c on pytest-dev:master.

[The-Compiler]

Looking at tup[1], it always seems to contain an unicode object, even when there are byte strings in the assertion:

-> exprinfo = str(tup[1])
(Pdb) tup[1]
AssertionError(u"assert 'a' == 'b'\n  - a\n  + b",)

So I think the proper fix would be to always use unicode() and do the check with u'assert ' below.

[nicoddemus]

Actually, tup[1] is an AssertionError instance containing a unicode string. I think the proper fix is actually using py._builtin._totext:

diff --git a/_pytest/_code/code.py b/_pytest/_code/code.py
index 040e4fc..9a6d326 100644
--- a/_pytest/_code/code.py
+++ b/_pytest/_code/code.py
@@ -354,7 +354,7 @@ class ExceptionInfo(object):
             if exprinfo is None and isinstance(tup[1], AssertionError):
                 exprinfo = getattr(tup[1], 'msg', None)
                 if exprinfo is None:
-                    exprinfo = str(tup[1])
+                    exprinfo = py._builtin._totext(tup[1])
                 if exprinfo and exprinfo.startswith('assert '):
                     self._striptext = 'AssertionError: '
         self._excinfo = tup

py._builtin._totext is just unicode in Python 2 and str in Python 3. With the above change the test passes to me.

[coveralls]

Coverage decreased (-0.02%) to 93.006% when pulling 6cbcc35 on AiOO:bugfix/assertion-with-unicode into 9c45d6c on pytest-dev:master.

[nicoddemus]

Nitpick: "has failed" or "fails" 😁

Also: Use double backticks around UnicodeEncodeError so it appears in a monospaced font (see buffer on the item above this one).

[AiOO]

Thanks for your kind review! I've updated this PR.

1. Use proper method py._builtin._totext instead of str or unicode.
2. Fix typo error and use backticks.

And,

do the check with u'assert ' below.

I think this fix is unnecessary because below code runs well:

Python 2.7.12 (default, Jun 29 2016, 14:05:02)
[GCC 4.2.1 Compatible Apple LLVM 7.3.0 (clang-703.0.31)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> u'assert: 유니코드'.startswith('assert: ')
True

[coveralls]

Coverage remained the same at 93.027% when pulling 86b8801 on AiOO:bugfix/assertion-with-unicode into 9c45d6c on pytest-dev:master.

[nicoddemus]

do the check with u'assert ' below.
I think this fix is unnecessary because below code runs well:

I agree. 😁

Thanks for the update, I will merge as soon as CI passes.

[nicoddemus]

Oh, just a tip: on GitHub if you add a string like "Fixes #XXX" or "Resolves #XXX" to the commit message it will automatically close the issue #XXX when merged. See here. 😉

[nicoddemus]

Thanks again for the PR!