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diffable_custom_matchers

📝 Leveraging diffable for Improved Failure Messages​

When comparing complex objects, adding diffable in your matcher enables side-by-side diffs on failure. You capture both expected and actual values, then let RSpec show granular differences automatically.

# spec/support/matchers/have_person_attributes.rb
RSpec::Matchers.define :have_person_attributes do |expected|
  match do |actual|
    @actual = actual.attributes.slice('name', 'age', 'email')
    @expected = expected.slice(:name, :age, :email)
    @actual == @expected
  end

  diffable

  failure_message do
    "expected person to have attributes #{expected.inspect}, but got #{@actual.inspect}"
  end
end

Usage:

person = Person.new(name: 'Alice', age: 30, email: 'a@example.com')
expect(person).to have_person_attributes(name: 'Bob', age: 30, email: 'a@example.com')