Project: RSpec Core 3.12

Publisher: RSpec

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.

Scenarios

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

Last published 4 months ago by Jon Rowe.

let and let!

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