[TIP] Struggling with pymock

Thomas Spreng spreng at socket.ch
Wed Sep 12 05:23:50 PDT 2007

Hash: SHA1

First of all, hi everybody (this is my first post on this list :))

Tobias Roth wrote:
> Now there's only one (I hope) problem left, I repeat it here for people
> not having to read the whole thread again:
> ** repetition **
> 1) The output [of pymock] is very unclear. I often get a 'raise
> PlaybackFailure("No
> further actions defined"', with no chance of finding out what went
> wrong. Consider the following example:
> s = open("file")
> for line in s:
>         pass
> s.close()
> For the open() and close() alone, I was able to get the test running as
> you suggested, by stubbing out __builtins__.open(). But when I add some
> reading, I always get the "No further actions defined". How do I find
> out what methods to record here? More detailed output from pymock would
> really help, especially when overriding stuff from libraries.
> ** end repetition **

not that I'm an expert in testing (let alone py-mocking ;)) but as far
as I know, you can use pymock's generator() method to turn a mock object
into a python generator. The problem using this approach is that I was
unable to record any other function calls on such a generator object.
Note that I'm not recording file.close() in the second test function. I
have no idea why verify() doesn't raise an exception in this case. Maybe
someone else can enlighten me? :)

Keep in mind, that it is also possible to just use a StringIO
(file-like) object instead of a mock object in your example.

Sample tests using both methods are shown below:

from pymock import *
from StringIO import StringIO

class Foo(object):

    def __init__(self, cf, opener=open):
        self.arg = []
        self.conffile = cf
        f = opener(self.conffile)
        for line in f:

class TestFoo(PyMockTestCase):

    path = "/path/to/nonexistant.txt"
    content = ["nothing", "to", "see", "here"]

    def testFooWithStringIO(self):
        file = StringIO('\n'.join(self.content))
        m = self.mock()
        self.expectAndReturn(m.open(self.path), file)
        # done recording, start testing
        f = Foo(self.path, m.open)
        self.assertEquals(f.arg, self.content)

    def testFooWithMockFile(self):
        m = self.mock()
        file = self.mock()
        self.expectAndReturn(m.open(self.path), file)
        self.generator(file, self.content)
        # done recording, start testing
        f = Foo(self.path, m.open)
        self.assertEquals(f.arg, self.content)
        # didn't record file.close(), why does
        # verify() not raise an exception?


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