On Sat, Dec 26, 2009 at 6:55 PM, David Chelimsky <dchelim...@gmail.com>wrote:
> On Sat, Dec 26, 2009 at 5:53 PM, Ed Howland <ed.howl...@gmail.com> wrote: > >> I hope this isn't a dumb question, but can a custom matcher be written >> for a possibly non-existant predicate? I know that if the object >> responds to some predicate? message, RSpec will breate a custom >> matcher on the fly for it. Such as be_naughty or be_nice for >> sarah.naughty? and jane.nice? >> > > It's not that RSpec looks at your code and creates predicates for it. When > you say "jane.should be_nice", RSpec looks to see if jane has a nice?() > method and uses that if it's there. Subtle, but important difference. > I should add here, that if you've already defined a be_nice method, it will be called. RSpec only checks for a predicate when it gets method_missing, which it wouldn't if you've defined a method already. HTH, David > > >> But what if you want to create your own where this is not the case. >> Like sarah.should_not be_on_santas_list: >> >> Spec::Matchers.define :be_on_santas_list do |expected| >> matcher do |actual| >> $santas_list.include? actual >> end >> end >> > > The block arguments should align with the arguments you pass to the > matcher. So if you intend to write this in the example: > > sarah.should_not be_on_santas_list > > Then the definition should be like this: > > Spec::Matchers.define :be_on_santas_list do > matcher do |actual| > $santas_list.include? actual > end > end > > ... with no block arguments. > > >> Or in the situation where the object has a predicate that returns a >> string and not true or false. As is the case with >> REXML::Document#stand_alone?: >> >> match do |actual| >> actual.stand_alone? == 'yes' >> end >> >> This works, but the value of expected is nil. >> > > That's because you didn't pass anything to the matcher, as described above. > > The fact that expected is nil at that point should not matter, since you're > not evaluating against expected in the match block. As long as as > "actual.stand_alone? == 'yes'" returns true or false (which it should unless > you've gone and redefined ==) you should be ok. > > >> Is this Ok? > > > Yes. Why do you ask? What are your concerns? What problems have you had? > > >> How do others handle this? . >> >> Thanks, and Happy Holidays. >> > > And to you. > > Cheers, > David > > >> Ed >> > >
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