Re-using Rspec Matchers

Hey Everyone,

Is it good practice to call matchers from within matchers? Kinda like
this pattern:

See: http://gist.github.com/570467


Brian

On Wed, Sep 8, 2010 at 14:42, Brian K. [email protected] wrote:

Is it good practice to call matchers from within matchers? Kinda like this pattern:

See: http://gist.github.com/570467

David C. taught me not to invoke #should in a matcher, but
rather just answer a boolean, so I expect that, rather than matcher
using matcher, you could extract the low-level matcher behavior into
methods that both matchers would use.

J. B. (Joe) Rainsberger :: http://www.jbrains.ca ::
http://blog.thecodewhisperer.com
Diaspar Software Services :: http://www.diasparsoftware.com
Author, JUnit Recipes
2005 Gordon Pask Award for contribution to Agile practice :: Agile
2010: Learn. Practice. Explore.

On Sep 8, 2010, at 2:17 PM, “J. B. Rainsberger” [email protected] wrote:

Okay thanks.

I’ll refractor matcher logic but was hoping I could be lazy and reuse /
cascade failure messages.


Brian

On Sep 8, 2010, at 5:19 PM, Brian K. wrote:

using matcher, you could extract the low-level matcher behavior into
methods that both matchers would use.

Okay thanks.

I’ll refractor matcher logic but was hoping I could be lazy and reuse / cascade failure messages.

You can :slight_smile:

The reason to avoid cascading matchers is they become somewhat useless
in the negative form (should_not). If you’re NEVER going to use them
that way, you’re fine cascading.

On 9/8/10 11:42 AM, Brian K. wrote:

Hey Everyone,

Is it good practice to call matchers from within matchers? Kinda like this pattern:

See: http://gist.github.com/570467

No, that should be avoided. The problem is that the “internal” matcher
will throw an exception that will bubble up and be reported. Meaning
that the parent matcher (link_one in your case) is not reported and the
resulting stacktrace can be confusing. Try something like this:

include_association(expected).matches?(actual) &&
associate_one(expected).matches?(actual)

(Note, I have not tried the above but I think it should work.)

-Ben

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