[TIP] RFC: Post-assertRaises assertions WAS: ANN: unittest2 0.4.0 Release

[Michael Foord]

On 09/04/2010 14:10, Olemis Lang wrote:
> On Thu, Apr 8, 2010 at 5:42 PM, Michael Foord<michael at voidspace.org.uk>  wrote:
>    
>> Hello all,
>>
>>      
> :o)
>
>    
>> I'm pleased to announce the release of version 0.4.0 of unittest2.
>>
>>      
> [...]
>    
>> For full details of all the new features, see my blog entry:
>>
>> * http://www.voidspace.org.uk/python/weblog/arch_d7_2010_04_03.shtml#e1171
>>
>>      
> I wanted to know if you have considered support for writing assertions
> targeting the exception object been raised . In my experience that is
> very helpful when testing some kind of systems. For instance, in Trac
> XmlRpcPlugin (<=0.1.6, current trunk ;o) you can find many tests
> (actually all TCs checking for error conditions ;o) like this
>
>    

Did you check the docs?

http://docs.python.org/dev/library/unittest.html#unittest.TestCase.assertRaises
http://www.voidspace.org.uk/python/articles/unittest2.shtml#assertraises

Michael


> {{{
> #!python
>
> class RpcXmlTestCase(unittest.TestCase):
>      # Further code omitted ;o)
>      def test_wrong_argspec(self):
>          try:
>              self.admin.system.listMethods("hello")
>              self.fail("Oops. Wrong argspec accepted???")
>          except xmlrpclib.Fault, e:
>              self.assertEquals(2, e.faultCode)
>              self.assertTrue("listMethods() takes exactly 2 arguments" \
>                                      in e.faultString)
>
> }}}
>
> The fact is that the exception object is needed to ensure proper error
> codes are returned by the RPC subsystem (and the current protocol
> handler under test, plugin is starting to adopt a pluggable
> architecture to support multiple RPC protocols ;o). Such assertions on
> exc objs will be used quite quite quite often. Nonetheless this
> specific style has some drawbacks e.g. assertion for failures are not
> explicit, other error conditions are reported as errors rather than
> failures, and ...
>
> Therefore, we're recently considering [1]_ (not committed yet ;o) to
> adopt this style
>
> {{{
> #!python
>
> class TracRpcTestCase(unittest.TestCase):
>          # Further code omitted ;o)
>          def assertRaises(self, excClass, callableObj, *args, **kwargs):
>              """Enhanced assertions to detect exceptions."""
>              try:
>                  callableObj(*args, **kwargs)
>              except excClass, e:
>                  return e
>              except self.failureException :
>                  raise
>              except Exception, e :
>                  if hasattr(excClass, '__name__'): excName = excClass.__name__
>                  else: excName = str(excClass)
>
>                  if hasattr(e, '__name__'): excMsg = e.__name__
>                  else: excMsg = str(e)
>
>                  raise self.failureException("\n\nExpected %s\n\nGot %s : %s" % (
>                                          excName, e.__class__.__name__, excMsg))
>              else:
>                  if hasattr(excClass,'__name__'): excName = excClass.__name__
>                  else: excName = str(excClass)
>                  raise self.failureException, "Expected %s\n\nNothing
> raised" % excName
>
> class RpcXmlTestCase(TracRpcTestCase):
>      # Further code omitted ;o)
>      def test_wrong_argspec(self):
>          def local_test():
>              self.admin.system.listMethods("hello")
>              self.fail("Oops. Wrong argspec accepted???")
>          e = self.assertRaises(xmlrpclib.Fault, local_test)
>          self.assertEquals(1, e.faultCode)
>          self.assertTrue("listMethods() takes exactly 2 arguments" \
>                                      in e.faultString)
>
> }}}
>
> ... using a customized `assertRaises` method that returns the
> exception object in order to perform further assertions ;o).
>
> This approach collides with context managers returned by modern
> `assertRaises` impl but AFAICS might be extremely useful in situations
> like the one I sketched above . Probably would be valuable to consider
> support for this in unittest(2) , what d'u think ?
>
> .. [1] TracRpc API v2 patch @ Bb
>           (http://bitbucket.org/osimons/trac-rpc-mq/src/tip/t5437/t5437-protocol_api_v2-r7194.diff)
>
>    


-- 
http://www.ironpythoninaction.com/
http://www.voidspace.org.uk/blog

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