Fix #913 for Serialize Matcher error undefined method `cast_type' in Rails 5

[bsodmike]

This patch is based on the discussed held in issue #913, and a solution
that I've proposed and others have confirmed as good to go 👏.

Oh, it also fixes spec breakage (for the existing spec).

Ref: #913 (comment)

[mcmire]

Thank you @bsodmike. I'm still here... I just haven't had a whole lot of time lately. But I will get to this.

[bsodmike]

@mcmire thanks - there seems to be an issue with CI. ta.

[aried3r]

I think it's because this PR does not differ between Rails 5 and 4 like the proposed patch in your comment. What do you think?

[bsodmike]

Also it doesn't seem like CI got very far?

Your bundle is complete!
It was installed into ./vendor/bundle
6.23s$ bundle exec rake
rake spec:unit --trace
** Invoke spec:unit (first_time)
** Execute spec:unit
Non shoulda-matchers warnings were raised during the test run. These have been written to /home/travis/build/thoughtbot/shoulda-matchers/tmp/irrelevant_warnings.txt.
All warnings were written to /home/travis/build/thoughtbot/shoulda-matchers/tmp/all_warnings.txt.
rake aborted!
Command failed with status (1): [rake spec:unit --trace...]
/home/travis/build/thoughtbot/shoulda-matchers/Rakefile:25:in `block in <top (required)>'
Tasks: TOP => default
(See full trace by running task with --trace)

This spec was broken locally if I set the version of Rails to 5.0.

[mcmire]

Usually when rake quits early like that and doesn't show any output it means that some file failed to load. Locally if you run, for instance, bundle exec appraisal 5.0 rake, then you may be able to see what's going on.

[DexterTheDragon]

I ran the tests for this PR locally and this is the error it's failing on

undefined method `active_model_lte_4?' for #<Class:0x00557be9b418f0> (NoMethodError)
Did you mean?  active_model_4_0?
               active_model_3_2?
               active_model_3_1?
        from shoulda-matchers/spec/unit/shoulda/matchers/active_model/allow_mass_assignment_of_matcher_spec.rb:4:in `block in <top (required)>'

This commit on the rails5 branch adds a call to the active_model_lte_4? method but it's not defined anywhere. 6c2fb57#diff-b8e72e4bed24a5c78f9bcc34440ba96bR4

If you look at the tests results for the rails5 branch in PR #960 it is failing the same way. The test failures would need to be resolved on the rails5 branch and then this fix rebased on to it.

Hopefully this help in moving along the Rails 5 support.

[mcmire]

Hey @bsodmike -- thanks so much for your PR, I apologize for the long delay in getting this in. We're still working on upgrading shoulda-matchers for Rails 5 but I've added this PR to the rails-5 branch here: 28a43a3. So I'm closing this so it doesn't clutter up the issues list. Thanks! 🎉