Project: RSpec Core 2.12

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.

Scenarios

use let to define memoized helper method

Given

a file named "let_spec.rb" with:

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

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

  it "is not cached across examples" do
    count.should 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
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
    invocation_order.should == [:let!, :example]
    count.should eq(1)
  end
end

When

I run rspec let_bang_spec.rb

Then

the examples should all pass

Last published over 5 years ago by dchelimsky.

let and let!

RSpec Core settings