RSpec: How to compare have_received arguments by object identity?

i used to using expect(subject/double).to haved_received(:a_method).with(args).exactly(n).times to test that a method be called with some specific arguments and be called exactly {n} times. But today it's broken with arguments are Comparable objects, take a look at the below code:

setup

class A; end

class B
 include Comparable
 attr_reader :val

 def initialize(val)
   @val = val
 end

 def <=>(other)
   self.val <=> other.val
 end
end

class S
 def call(x); end
end

s = S.new
allow(s).to receive(:call)

now the below test passed with normal object A

a1 = A.new
a2 = A.new

s.call(a1)
s.call(a2)

expect(s).to have_received(:call).with(a1).exactly(1).times
expect(s).to have_received(:call).with(a2).exactly(1).times

but it failed with Comparable object B

b1 = B.new(0)
b2 = B.new(0)

s.call(b1)
s.call(b2)

expect(s).to have_received(:call).with(b1).exactly(1).times
expect(s).to have_received(:call).with(b2).exactly(1).times

i debug and saw that the rspec matcher call the spaceship operator <=> to verify arguments, so it considers b1 and b2 are the same

Failure/Error: expect(s).to have_received(:call).with(b1).exactly(1).times
expected: 1 time with arguments:
received: 2 times with arguments:

What should i do to pass the test ?

Solution

This happens because Comparable implements ==, so your objects are treated as being equal in regards to ==:

b1 = B.new(0)
b2 = B.new(0)

b1 == b2 #=> true

To set a constraint based on object identity, you can use the equal matcher: (or its aliases an_object_equal_to / equal_to)

expect(s).to have_received(:call).with(an_object_equal_to(b1)).once

Under the hood, this matcher calls equal?:

b1 = B.new(0)
b2 = B.new(0)

b1.equal?(b2) #=> false