Question

I am trying to use python’s unittest library to write some unit tests. I have a function that returns an unordered list of objects. I want to verify that the objects are the same, and I am trying to use assertCountEqual to do this.

However, this seems to be failing, despite the individual objects being equal (==) to each other. Here is the ‘diff’ output from the assertion failure:

First has 1, Second has 0:  Intersection(time=8.033252939677466e-08, del_time=8.033252939677466e-08, pos=Vector(10.00, 0.00), line=Line(Vector(500.00, 0.00), Vector(0.00, 0.00)), ent=None, oth=None, invalid=False)
First has 1, Second has 0:  Intersection(time=-9.918729244820295e-16, del_time=-9.918729244820295e-16, pos=Vector(10.00, 0.00), line=Line(Vector(500.00, 0.00), Vector(0.00, 0.00)), ent=None, oth=None, invalid=False)
First has 0, Second has 1:  Intersection(time=8.033252939677466e-08, del_time=8.033252939677466e-08, pos=Vector(10.00, 0.00), line=Line(Vector(500.00, 0.00), Vector(0.00, 0.00)), ent=None, oth=None, invalid=False)
First has 0, Second has 1:  Intersection(time=-9.918729244820295e-16, del_time=-9.918729244820295e-16, pos=Vector(10.00, 0.00), line=Line(Vector(500.00, 0.00), Vector(0.00, 0.00)), ent=None, oth=None, invalid=False)

Verifying that they are equal:

>>> i = Intersection(time=8.033252939677466e-08, del_time=8.033252939677466e-08, pos=Vector(10.00, 0.00), line=Line(Vector(500.00, 0.00), Vector(0.00, 0.00)), ent=None, oth=None, invalid=False)
>>> j = Intersection(time=8.033252939677466e-08, del_time=8.033252939677466e-08, pos=Vector(10.00, 0.00), line=Line(Vector(500.00, 0.00), Vector(0.00, 0.00)), ent=None, oth=None, invalid=False)
>>> i == j
True
>>> i = Intersection(time=-9.918729244820295e-16, del_time=-9.918729244820295e-16, pos=Vector(10.00, 0.00), line=Line(Vector(500.00, 0.00), Vector(0.00, 0.00)), ent=None, oth=None, invalid=False)
>>> j = Intersection(time=-9.918729244820295e-16, del_time=-9.918729244820295e-16, pos=Vector(10.00, 0.00), line=Line(Vector(500.00, 0.00), Vector(0.00, 0.00)), ent=None, oth=None, invalid=False)
>>> i == j
True

My guess is that the assertCountEqual function is checking if the two have the same identity (e.g. i is j), rather than equality.

• Is there a unittest function that will provide the same diff
  capabilities, but use equality comparison, rather than identity?
• Alternatively, is there some way I can write a function that performs
  similarly to assertCountEqual?

EDIT: I am running python 3.2.2.

Answer 1

you can look for yourself how the comparison is done:

• generate a list from each iterable
• use a collections.Counter to count the objects – works only for hashable elements
• if the elements are not hashable, compare them directly

as your Intersections are objects, they are hashable per default, but if you don’t provide a suitable hash function (which you should do if you provide comparison methods) they will be considered different.

so, does your Intersection class fullfill the hash contract?