RSpec -- test if method called its block parameter

Question

I have a method that takes block of code as an argument. The problem is: how to test using RSpec if this method called the block?

The block may be evaluated in any scope the method needs, not necessarily using a yield or block.call. It be passed to another class, or evaluated it in an anonymous class object or somewhere else. For the test to pass it is enough to evaluate the block somewhere as a result of the method call.

Is there a way to test something like this using RSpec?

See also this for more complex case with lets and mocks.

Create a block with a side effect, like setting an enclosed variable our raising an exception, and check for the side effect? — Dave Newton, Nov 06 '12 at 10:56
Thanks for the idea! Especially the concept with an exception is promising in this case. — wrzasa, Nov 06 '12 at 14:12

score 3 · Answer 1 · answered Aug 23 '14 at 15:07

I like using throw instead of raise for this sort of problem, because it can't be rescued be an arbitrary rescue handler. So it might look like this:

my_proc = proc { throw :my_proc_was_called }
expect {
  my_proc.call
}.to throw_symbol :my_proc_was_called

score 2 · Accepted Answer · edited Feb 28 '16 at 11:47

2

I usually do something like

a = 1
b.go { a = 2}
a.should == 2

edited Feb 28 '16 at 11:47

Arturo Herrero

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answered Nov 06 '12 at 17:07

rogerdpack

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This one works too! Simple and effective! Thanks ;-) Also added additional message to the `should` test to prevent confusion, like [here](http://stackoverflow.com/questions/4183656/how-to-attach-message-to-rspec-check) – wrzasa Nov 07 '12 at 10:26

score 1 · Answer 3 · answered Nov 06 '12 at 15:06

Thanks to Dave Newton's suggestion in the comment above I did something like this:

 it "should run block defining the node" do
   message="This message is raised if block is properly evaluated."
   expect do
     node do
       raise message
     end 
   end.to raise_error message
 end

In case of error this prints message:

 Failure/Error: expect do
   expected Exception with "This message is raised if block is properly evaluated." but nothing was raised

Which I find informative enough.

Thanks again for help!

RSpec -- test if method called its block parameter

3 Answers3

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