gistfile1.txt

def bar
  puts "welp"
end

def foo
  bar
end

RSpec.describe "foo" do
  it "calls bar" do
    expect(self).to receive(:bar)
    foo
  end
end

Hey, thanks! it worked.
I had tried the following:

s = double(self)
average(numbers: [3,5,2])
expect(s).to have_received(:sum).with(numbers: [3,5,2])

But that failed with
Failure/Error: expect(s).to have_received(:sum).with(numbers: [3,5,2]) Double #<RSpec::ExampleGroups::Average:0x007fa281b1dbd8 @__memoized=nil> expected to have received sum, but that object is not a spy or method has not been stubbed.

@itgsoddabe the double is a different object, so it doesn't receive anything. If you want to use the have_received style of expectation you'd do this:

allow(self).to receive(:sum)
average(numbers: [3,5,2])
expect(self).to have_received(:sum).with (numbers: [3,5,2])

If you do want to use the double you could also do this:

s = double()
s.average(numbers: [3,5,2])
expect(s).to have_received(:sum).with (numbers: [3,5,2])