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let and let!

Use let to define a memoized helper method. The value will be cached across multiple calls in the same example but not across examples.

Note that let is lazy-evaluated: it is not evaluated until the first time the method it defines is invoked. You can use let! to force the method's invocation before each example.

By default, let is threadsafe, but you can configure it not to be by disabling config.threadsafe, which makes let perform a bit faster.

Use let to define memoized helper method​

Given a file named "let_spec.rb" with:

$count = 0
RSpec.describe "let" do
  let(:count) { $count += 1 }

  it "memoizes the value" do
    expect(count).to eq(1)
    expect(count).to eq(1)
  end

  it "is not cached across examples" do
    expect(count).to eq(2)
  end
end

When I run rspec let_spec.rb

Then the examples should all pass.

Use let! to define a memoized helper method that is called in a before hook​

Given a file named "let_bang_spec.rb" with:

$count = 0
RSpec.describe "let!" do
  invocation_order = []

  let!(:count) do
    invocation_order << :let!
    $count += 1
  end

  it "calls the helper method in a before hook" do
    invocation_order << :example
    expect(invocation_order).to eq([:let!, :example])
    expect(count).to eq(1)
  end
end

When I run rspec let_bang_spec.rb

Then the examples should all pass.