Implicit docstrings

When you use rspec-expectations with rspec-core, RSpec is able to auto-generate the docstrings for examples for you based on the last expectation in the example. This can be handy when the matcher expresses exactly what you would write in your example docstring, but it can also be easily abused. We find that the freeform nature of the docstring provides a lot of value when used well (e.g. to document the “why” of a particular behavior), and you lose that kind of flexibility when you rely on the matcher to generate the docstring for you.

In general, we recommend only using this feature when the matcher aligns exactly with the docstring you would write. Even then, many users prefer the explicitness of the full docstring, so use this feature with care (if at all).

Run passing examples

Given a file named “implicitdocstringsspec.rb” with:

RSpec.describe "Examples with no docstrings generate their own:" do
  specify { expect(3).to be < 5 }
  specify { expect([1,2,3]).to include(2) }
  specify { expect([1,2,3]).to respond_to(:size) }
end

When I run rspec ./implicit_docstrings_spec.rb -fdoc

Then the output should contain “is expected to be < 5”

And the output should contain “is expected to include 2”

And the output should contain “is expected to respond to #size”.

Run failing examples

Given a file named “failingimplicitdocstrings_spec.rb” with:

RSpec.describe "Failing examples with no descriptions" do
  # description is auto-generated per the last executed expectation
  specify do
    expect(3).to equal(2)
    expect(5).to equal(5)
  end

  specify { expect(3).to be > 5 }
  specify { expect([1,2,3]).to include(4) }
  specify { expect([1,2,3]).not_to respond_to(:size) }
end

When I run rspec ./failing_implicit_docstrings_spec.rb -fdoc

Then the output should contain “is expected to equal 2”

And the output should contain “is expected to be > 5”

And the output should contain “is expected to include 4”

And the output should contain “is expected not to respond to #size”.