# Assert\_no\_difference question

**URL:** <https://www.ruby-forum.com/t/assert-no-difference-question/137491>\
**Category:** Rails\
**Created:** [May 13, 2008, 5:21pm UTC](https://www.ruby-forum.com/t/assert-no-difference-question/137491 "2008-05-13T17:21:28Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![tcsnide](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/eb8c5e/32.png) [@tcsnide](https://www.ruby-forum.com/u/tcsnide)\
**Post date:** [May 13, 2008, 5:21pm UTC](https://www.ruby-forum.com/t/assert-no-difference-question/137491/1 "2008-05-13T17:21:28Z")

</div>

I have the following test code:

assert\_no\_difference Avatar, :count do  
a = create\_avatar(:description =\> nil)  
assert a.errors.on(:description)  
end

further down, create\_avatar looks like:

def create\_avatar(options = {})  
Avatar.create(:description =\> “Foo Descr.”).merge(options)  
end

(Borrowed from the user test in acts\_as\_auth…)

It seems to pass, as my avatar model has:

validates\_presence\_of :description written.

However, if say I try to force it to fail with assert\_difference… it  
still passes.

What did I miss?