Customer matcher diff and failure message help

[Arup Rakshit]

Hi,

I am trying to write a custom matcher, but not able to show the diff and error message correctly. I need help with it.

RSpec::Matchers.define :have_constant do |const|

  match do |owner|

    owner.const_defined?(const) && owner.const_get(const) == @second

  end

  chain :with_value do |second|

    @second = second

  end

  diffable

  failure_message do |actual|

    "expected that #{const} would be defined in #{actual} with #{@second}"

  end

end

And the spec is:

describe "FeatureService" do

  describe 'constants' do

    subject { FeatureService }

    it { is_expected.to have_constant(:IMO_NUMBER_VALIDATION).with_value('6cjXBWdq') }

    it { is_expected.to have_constant(:JOB_TYPES).with_value('6cjXBWdq') }

    # ...

  end

end

The actual class is:

class FeatureService

  JOB_TYPES = 'WN2HsoIm'.freeze

  #...

end

When I run the test the failure message is not quiet helpful. So how can I tweak the custom matcher so that it can be helpful when it writes to stdout than what I see currently.

$ rspec ./spec/services/feature_service_spec.rb:8

Run options: include {:locations=>{"./spec/services/feature_service_spec.rb"=>[8]}}

F

Failures:

  1) FeatureService constants should have constant :JOB_TYPES with value "6cjXBWdq"

     Failure/Error: it { is_expected.to have_constant(:JOB_TYPES).with_value('6cjXBWdq') }

     

       expected that JOB_TYPES would be defined in FeatureService with 6cjXBWdq

       Diff:

       @@ -1,2 +1,2 @@

       -:JOB_TYPES

       +FeatureService

       

     # ./spec/services/feature_service_spec.rb:8:in `block (3 levels) in <top (required)>'

[Jon Rowe]

Hi Arup

You need to define `expected` and `actual` to surface the variables you wish to diff. In your case `expected` should be `@second` and `actual` should be `owner.const_defined?(const) && owner.const_get(const)`.

See the matcher protocol documentation for more information.

http://rspec.info/documentation/3.8/rspec-expectations/RSpec/Matchers/MatcherProtocol.html#diffable%3F-instance_method

Cheers

Jon Rowe

---------------------------

ma...@jonrowe.co.uk

jonrowe.co.uk

[Arup Rakshit]

Hello Jon,

Thanks for your reply.

I modified it as:

RSpec::Matchers.define :have_constant do |const|

    match do |owner|

      @actual = owner.const_defined?(const) && owner.const_get(const)

      @expected = @second

      owner.const_defined?(const) && owner.const_get(const) == @second

    end

    chain :with_value do |second|

      @second = second

    end

    diffable

    failure_message do |actual|

      "expected that #{const} would be defined with #{actual} but got #{@second}"

    end

  end

Now the error message is close, but not quiet correct.

Failures:

  1) FeatureService constants should have constant :TABLE_OF_PREVIOUS_INSPECTIONS with value "3oelqiFW1"

     Failure/Error: it { is_expected.to have_constant(:TABLE_OF_PREVIOUS_INSPECTIONS).with_value('3oelqiFW1') }

     

       expected that TABLE_OF_PREVIOUS_INSPECTIONS would be defined with 3oelqiFW but got 3oelqiFW1

       Diff:

       @@ -1,2 +1,2 @@

       -:TABLE_OF_PREVIOUS_INSPECTIONS

       +"3oelqiFW"

I want it to be like:

Failures:

  1) FeatureService constants should have constant :TABLE_OF_PREVIOUS_INSPECTIONS with value "3oelqiFW1"

     Failure/Error: it { is_expected.to have_constant(:TABLE_OF_PREVIOUS_INSPECTIONS).with_value('3oelqiFW1') }

     

       expected that TABLE_OF_PREVIOUS_INSPECTIONS would be defined with 3oelqiFW but got 3oelqiFW1

       Diff:

       @@ -1,2 +1,2 @@

       -"3oelqiFW1"

       +"3oelqiFW"

What needs to be tweaked ?

[Jon Rowe]

I believe you still need to defined expected, also I think you have `actual` and `@second` the wrong way around in your description.

Jon Rowe

---------------------------

ma...@jonrowe.co.uk

jonrowe.co.uk

[Arup Rakshit]

Hm, I am confused too. Which part i need to change? Not sure from where the symbol is coming though.

[Jon Rowe]

As I said, you need to define the methods, e.g not the instance variables, they are considered “private” and are not called what you expect in this case.

This does what you want:

RSpec::Matchers.define :have_constant do |const|

  match do |owner|

    @actual_value = owner.const_defined?(const) && owner.const_get(const)

    actual == expected

  end

  def actual

    @actual_value

  end

  def expected

    raise ArgumentError, "expected value not set" unless @expected_value

    @expected_value

  end

  chain :with_value do |second|

    @expected_value = second

  end

  diffable

  failure_message do

    "expected that #{const} would be defined with #{expected} but got #{actual}"

  end

end

Cheers

Jon Rowe

---------------------------

ma...@jonrowe.co.uk

jonrowe.co.uk

On 13 May 2019 at 10:56, Arup Rakshit wrote:

[Arup Rakshit]

I just added your code and run the test intentionally to see the failure message. But there is no diff printed.

rspec ./spec/services/feature_service_spec.rb

.....F.

Failures:

  1) FeatureService constants should have constant "3oelqiFW1" with value "3oelqiFW1"

     Failure/Error: it { is_expected.to have_constant(:TABLE_OF_PREVIOUS_INSPECTIONS).with_value('3oelqiFW1') }

       expected that TABLE_OF_PREVIOUS_INSPECTIONS would be defined with 3oelqiFW1 but got 3oelqiFW

     # ./spec/services/feature_service_spec.rb:12:in `block (3 levels) in <top (required)>'

     # ./spec/rails_helper.rb:41:in `block (3 levels) in <top (required)>'

     # /Users/aruprakshit/.rvm/gems/ruby-2.3.3@DockingTestApp/gems/database_cleaner-1.6.1/lib/database_cleaner/generic/base.rb:16:in `cleaning'

     # /Users/aruprakshit/.rvm/gems/ruby-2.3.3@DockingTestApp/gems/database_cleaner-1.6.1/lib/database_cleaner/base.rb:98:in `cleaning'

     # /Users/aruprakshit/.rvm/gems/ruby-2.3.3@DockingTestApp/gems/database_cleaner-1.6.1/lib/database_cleaner/configuration.rb:86:in `block (2 levels) in cleaning'

     # /Users/aruprakshit/.rvm/gems/ruby-2.3.3@DockingTestApp/gems/database_cleaner-1.6.1/lib/database_cleaner/configuration.rb:87:in `cleaning'

     # ./spec/rails_helper.rb:40:in `block (2 levels) in <top (required)>'

Finished in 0.47436 seconds (files took 10.93 seconds to load)

7 examples, 1 failure

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[Jon Rowe]

Hi Arup

Yes thats correct, we don’t diff single line strings as there changes are covered in the overall failure.

Cheers

Jon Rowe

---------------------------

ma...@jonrowe.co.uk

jonrowe.co.uk