Using Let and Context to Modularize RSpec Tests

When test suites contain a lot of duplication, coupling occurs at an individual spec basis. By utilizing core RSpec functionality, developers can clean up specs in order to reduce duplication and add clarity to the focal point of the spec.

Ally Piechowski · Dec 23, 2019 · 2 min read

Using Let and Context to Modularize RSpec Tests

If I want to test an invalid and valid email, it’s pretty easy to test with a basic RSpec test:

RSpec.describe User do
  it '[email protected] is a valid email' do
    expect(
        User.new(
          name: 'John Doe',
          email: '[email protected]',
          phone: '555-555-5555'
        )
    ).to be_valid
  end
  
  it 'johnatexampledotcom is not a valid email' do
    expect(
      User.new(
        name: 'John Doe',
        email: 'johnatexampledotcom',
        phone: '555-555-5555'
      )
  ).to_not be_valid
  end
end

While this may work for the first few specs, this starts to get a bit tedious and duplicative.

This is not optimal because our setup code has a lot of duplication and this duplicated code.

The RSpec Let + Context Pattern

By using core Rspec functionality, we can spruce up these 2 tests like so:

RSpec.describe User do
  subject do
    User.new(
      name: 'John Doe',
      email: email,
      phone: '555-555-5555'
    )
  end
  let(:email) { '[email protected]' }

  context 'when email is [email protected]' do
    let(:email) { '[email protected]' }

    it do
      expect(subject).to be_valid
    end
  end

  context 'when email is testfakeemail (does not contain @)' do
    let(:email) { 'testfakeemail' }

    it do
      expect(subject).to_not be_valid
    end
  end
end

This provides us with:

DRY specs
Re-usable setup code
- Additional specs within each context
- New specs, such as “phone number validations”
Easily interpretable differences between specs

The context / let pattern brings the most clarity into the differences between the 2 tests. This pattern can be used with in combination with Factories in order to make my tests extra clear and extra dry. Additionally, this pattern typically results in a more thoughtful test output.

The RSpec Let + Context Pattern

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