RSpec matcher that checks collection to include item that satisfies lambda

Question

I am a bit at a loss as to how to write a RSpec 3.2.x spec that checks wether a list contains at least one item that satisfies a condition.

Here is an example:

model = Invoice.new
model.name = 'test'
changes = model.changes
expect(changes).to include { |x| x.key == 'name' && x.value == 'test' }

There will be other (automated) changes in the changes list too so I don't want to verify that there is only one specific change and I also don't want to rely on ordering expect(changes.first)... so I basically need a way to specify that at least one change in the list satisfies the condition.

I could do something like this:

result = changes.any? { |x| x.key == 'name' .. }
expect(result).to eq(true)

But then the rspec failure would not give me any meaningful output so I thought there must be a built-in way to match this.

Any other suggestions on how to structure the test are also welcome.

Edit: To be clear - the changes are a list of ChangeObject so I need to access their .key and .value method

Answer 1

In RSpec 3, matchers are fully composable, which means you can pass any object which implements Ruby's === protocol (including a matcher!) to include and it will work properly. Lambdas in Ruby 1.9 implement the === protocol, which means you can do this:

expect(changes).to include(lambda { |x| x.key == 'name' && value == 'test' })

That said, that's not going to give you a great failure message (since RSpec has no way to generate a description of the lambda). I'm not sure where value comes from in your example, but if it is intended to be x.value, you could use the have_attributes (or an_object_having_attributes for better readability) matcher:

expect(changes).to include an_object_having_attributes(key: 'name', value: 'test')

Answer 2

Try this

expect(changes).to be_any{ |x| //logic to match }