New submission from Nick Coghlan:
When creating the error handling tests for the new ipaddress module, one of the
things I added was an "assertCleanError" method on the test cases [1].
This is a wrapper around assertRaisesRegex which ensures that either no
exception context is set, or if there is one set, ensures that the display is
suppressed by default.
While I don't think assertCleanError itself is suitable for adoption (there are
two many use case specific details), I think it *would* be useful to provide
two related helper assertions along the lines of the following (the failure
message in the first case could likely be improved).
Firstly, ensuring that the context has been *suppressed* when it should have
been:
def assertCleanTraceback(self, exc, msg=None):
exc_context = exc.__context__
if exc_context is not None and not exc.__suppress_context__:
if msg is None:
fmt = "{} has context set: {}"
msg = fmt.format(type(exc), type(exc_context))
self.fail(msg)
return exc_context
and secondly ensuring that the cause has been *set* when it should have been:
def assertRaisedFrom(self, exc, expected_cause, expected_regex, msg=None):
exc_cause = exc.__cause__
# Use the guts of assertRaises to compare the actual cause
# and the expected cause and raise an appropriate failure
# if they don't match
return exc_cause
Both proposed helpers return the actual context/cause so they can be used to
test longer deliberate exception chaings.
[1]
http://hg.python.org/cpython/file/04ca3f1515cf/Lib/test/test_ipaddress.py#l37
----------
messages: 189945
nosy: michael.foord, ncoghlan
priority: normal
severity: normal
stage: needs patch
status: open
title: Add more exception related assertions to unittest
type: enhancement
versions: Python 3.4
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Python tracker <[email protected]>
<http://bugs.python.org/issue18054>
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