RSpec is_anticipated helper

This is about a little helper method called is_anticipated which complements is_expected — a trial to make RSpec even nicer.

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RSpec is a testing framework for Ruby. It has a long history and it’s incredibly powerful. For tests which have a lot of context switches you may use the one-liner syntax. So you may write concise tests like these:

describe '#apply' do
  subject { described_class.new(params).apply(products) }

  let(:products) { Product.all }

  context 'when not filtering' do
    before do
      create(:product, name_de: 'A')
      create(:product, name_de: 'B')
      create(:product, name_de: 'C')
    end

    let(:params) { {} }

    it { is_expected.to match_array(products) }
  end

  context 'when filtering via options (type 2, 7)' do
    before { … }

    let(:params) { { … } }

    it { is_expected.to find_products('B', 'C') }
  end
end

This may need a bit of practice to get used to, mainly because you may not immediately see the “act”-part of the test — it’s nested in the subject.

The problem

Now there’s a problem with the one-liner syntax, as stated in the docs:

The one-liner syntax only works with non-block expectations

This means you could not write a test like this (using db-query-matchers gem):

describe '#apply' do
  subject { described_class.new(params).apply(products) }
  …
  it { is_expected.not_to make_database_queries }
end

It would raise an error like this:

Failure/Error: it { is_expected.not_to make_database_queries }
TypeError:
       wrong argument type … (expected Proc)

The solution

I often introduce my little helper method is_anticipated into projects. The very simple setup looks like this:

# spec/support/is_anticipated.rb
module IsAnticipated
  def is_anticipated
    expect { subject }
  end
end
# spec/rails_helper.rb
RSpec.configure do |config|
  config.include IsAnticipated
end

With that in place the following test works like a charm:

describe '#apply' do
  subject { described_class.new(params).apply(products) }
  …
  it { is_anticipated.not_to make_database_queries }
end

Why is_anticipated ?

Because “anticipate” means to expect something and take action in expectation while “expect” means regard as likely to happen and does not require any action.

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