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Project: RSpec Core 3.0

Publisher: RSpec

explicit subject

Use subject in the group scope to explicitly define the value that is
returned by the subject method in the example scope.

Note that while the examples below demonstrate how subject can be used as a
user-facing concept, we recommend that you reserve it for support of custom
matchers and/or extension libraries that hide its use from examples.

Scenarios
  1. `subject` in top level group
  2. `subject` in a nested group
  3. Access `subject` from `before` block
  4. Invoke helper method from `subject` block
  5. `subject` block is invoked at most once per example
  6. `subject!` bang method
`subject` in top level group
Given
a file named "top_level_subject_spec.rb" with: 
RSpec.describe Array, "with some elements" do
  subject { [1,2,3] }
  it "should have the prescribed elements" do
    expect(subject).to eq([1,2,3])
  end
end
When
I run rspec top_level_subject_spec.rb
Then
the examples should all pass
`subject` in a nested group
Given
a file named "nested_subject_spec.rb" with: 
RSpec.describe Array do
  subject { [1,2,3] }
  describe "with some elements" do
    it "should have the prescribed elements" do
      expect(subject).to eq([1,2,3])
    end
  end
end
When
I run rspec nested_subject_spec.rb
Then
the examples should all pass
Access `subject` from `before` block
Given
a file named "top_level_subject_spec.rb" with: 
RSpec.describe Array, "with some elements" do
  subject { [] }
  before { subject.push(1,2,3) }
  it "should have the prescribed elements" do
    expect(subject).to eq([1,2,3])
  end
end
When
I run rspec top_level_subject_spec.rb
Then
the examples should all pass
Invoke helper method from `subject` block
Given
a file named "helper_subject_spec.rb" with: 
RSpec.describe Array do
  def prepared_array; [1,2,3] end
  subject { prepared_array }
  describe "with some elements" do
    it "should have the prescribed elements" do
      expect(subject).to eq([1,2,3])
    end
  end
end
When
I run rspec helper_subject_spec.rb
Then
the examples should all pass
`subject` block is invoked at most once per example
Given
a file named "nil_subject_spec.rb" with: 
RSpec.describe Array do
  describe "#[]" do
    context "with index out of bounds" do
      before { expect(Array).to receive(:one_two_three).once.and_return([1,2,3]) }
      subject { Array.one_two_three[42] }
      it { is_expected.to be_nil }
    end
  end
end
When
I run rspec nil_subject_spec.rb
Then
the examples should all pass
`subject!` bang method
Given
a file named "subject_bang_spec.rb" with: 
RSpec.describe Array do
  describe '#pop' do
    let(:prepared_array) { [1,2,3] }
    subject! { prepared_array.pop }
    it "removes the last value from the array" do
      expect(prepared_array).to eq([1,2])
    end
    it "returns the last value of the array" do
      expect(subject).to eq(3)
    end
  end
end
When
I run rspec subject_bang_spec.rb
Then
the examples should all pass

Last published about 6 years ago by myronmarston.