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Project: RSpec Core 3.0

One-liner syntax

  • @oneliner-should

RSpec supports a one-liner syntax for setting an expectation on the
subject. RSpec will give the examples a doc string that is auto-
generated from the matcher used in the example. This is designed specifically
to help avoid duplication in situations where the doc string and the matcher
used in the example mirror each other exactly. When used excessively, it can
produce documentation output that does not read well or contribute to
understanding the object you are describing.

This comes in two flavors:

  • is_expected is defined simply as expect(subject) and is designed for when you are using rspec-expectations with its newer expect-based syntax.
  • should was designed back when rspec-expectations only had a should-based syntax. However, it continues to be available and work even if the :should syntax is disabled (since that merely removes Object#should but this is RSpec::Core::ExampleGroup#should).

Note: this feature is only available when using rspec-expectations.

Scenarios
Implicit subject
Given
a file named "example_spec.rb" with:
RSpec.describe Array do
  describe "when first created" do
    # Rather than:
    # it "should be empty" do
    #   subject.should be_empty
    # end

    it { should be_empty }
    # or
    it { is_expected.to be_empty }
  end
end
When
I run rspec example_spec.rb --format doc
Then
the examples should all pass
And
the output should contain:
Array
  when first created
    should be empty
    should be empty
Explicit subject
Given
a file named "example_spec.rb" with:
RSpec.describe Array do
  describe "with 3 items" do
    subject { [1,2,3] }
    it { should_not be_empty }
    # or
    it { is_expected.not_to be_empty }
  end
end
When
I run rspec example_spec.rb --format doc
Then
the examples should all pass
And
the output should contain:
Array
  with 3 items
    should not be empty
    should not be empty

Last published 10 months ago by myronmarston.