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Project: RSpec Expectations 3.8

define diffable matcher

When a matcher is defined as diffable, the output will include a diff of the submitted objects when the objects are more than simple primitives.

Scenarios
define a diffable matcher
Given
a file named "diffable_matcher_spec.rb" with:
RSpec::Matchers.define :be_just_like do |expected|
  match do |actual|
    actual == expected
  end

  diffable
end

RSpec.describe "two\nlines" do
  it { is_expected.to be_just_like("three\nlines") }
end
When
I run rspec ./diffable_matcher_spec.rb
Then
it should fail with:
       Diff:
       @@ -1,3 +1,3 @@
       -three
       +two
        lines
Redefine actual

Sometimes is neccessary to overwrite actual to make diffing work, e.g. if actual is a name of a file you want to read from. For this to work you need to overwrite @actual in your matcher.

Given
a file named "redefine_actual_matcher_spec.rb" with:
RSpec::Matchers.define :have_content do |expected|
  match do |actual|
    @actual = File.read(actual).chomp

    values_match? expected, @actual
  end

  diffable
end

RSpec.describe 'Compare files' do
  context 'when content is equal' do
    it { expect('data.txt').to have_content 'Data' }
  end

  context 'when files are different' do
    it { expect('data.txt').to have_content "No\nData\nhere" }
  end
end
And
a file named "data.txt" with:
Data
When
I run rspec ./redefine_actual_matcher_spec.rb --format documentation
Then
the exit status should not be 0
And
the output should contain:
2 examples, 1 failure
And
the output should contain:
       @@ -1,4 +1,2 @@
       -No
        Data
       -here

Last published 3 months ago by myronmarston.