Project: RSpec Core 3.0

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.

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 about 2 years ago by myronmarston.

let and let!

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