after.diff

Failures:

  1)  should custom match false
     Failure/Error: expect(true).to custom_match(false)
       expected true to custom match false
     # ./matcher_spec.rb:12:in `block (2 levels) in <top (required)>'

  2)  should custom match "another"
     Failure/Error: expect("string").to custom_match("another")
       expected "string" to custom match "another"
     # ./matcher_spec.rb:15:in `block (2 levels) in <top (required)>'

Finished in 0.0006 seconds
2 examples, 2 failures

before.diff

Failures:

  1)  should custom match false
     Failure/Error: expect(true).to custom_match(false)
       expected true to custom match false
       Diff:
       @@ -1,2 +1,2 @@
       -[false]
       +true
     # ./matcher_spec.rb:12:in `block (2 levels) in <top (required)>'

  2)  should custom match "another"
     Failure/Error: expect("string").to custom_match("another")
       expected "string" to custom match "another"
     # ./matcher_spec.rb:15:in `block (2 levels) in <top (required)>'

Finished in 0.0006 seconds
2 examples, 2 failures

custom_match_diff_spec.rb

RSpec::Matchers.define :custom_match do |expected|
  match do |actual|
    actual == expected
  end
  diffable
end

describe do
  example do
    expect(true).to custom_match(false)
  end
  example do
    expect("string").to custom_match("another")
  end
end