change_matcher_spec.rb

require 'rspec'

class Thing; end

describe "change matcher" do
  it "behaves counterintuitively with classes" do
    thing = nil
    expect {
      thing = Thing
    }.to change {
      thing
    }.from(nil).to(Thing)
  end
end

output.txt

$ rspec change_matcher_spec.rb 
F

Failures:

  1) change matcher behaves counterintuitively with classes
     Failure/Error: expect {
       result should have been changed to Thing, but is now Thing
     # ./rspec_change_behaviour_spec.rb:8:in `block (2 levels) in <top (required)>'

Finished in 0.00233 seconds
1 example, 1 failure