Enable diffing for RSpec array matcher

Question

RSpec provides a "diff"-style output when comparing multi-line strings. Is there a way to do something similar when comparing arrays (other than converting the array to a multi-line string)?

Answer 1

I may be mistaken, but I don't think this feature is built-in to RSpec.

However, you could implement a custom matcher with a custom error message:

RSpec::Matchers.define(:eq_array) do |expected|
  match { |actual| expected == actual }

  failure_message do |actual|
    <<~MESSAGE
      expected: #{expected}
      got:      #{actual}

      diff:     #{Diffy::Diff.new(expected.to_s, actual.to_s).to_s(:color)}
    MESSAGE
  end
end

# Usage:

expect([1, 2, 3]).to eq_array([1, 4, 3])

This demo is using the diffy library; you could implement this however you see fit.