what is the scope of 'let' in Rspec?

Question

I tried the following:

  describe "#check_recurring_and_send_message" do

    let(:schedule) {ScheduleKaya.new('test-client-id')}

    context "when it is 11AM and recurring event time is 10AM" do

      schedule.create_recurring_event('test-keyword', 'slack', 'day', '10 AM') 

      it "sends an SMS" do

      end

      it "set the next_occurrence to be for 10AM tomorrow" do 
        tomorrow = Chronic.parse("tomorrow at 10AM")
        expect(schedule.next_occurrence).to eq(tomorrow)
      end

    end

  end

I got an error around the scope:

`method_missing': `schedule` is not available on an example group (e.g. a `describe` or `context` block). It is only available from within individual examples (e.g. `it` blocks) or from constructs that run in the scope of an example (e.g. `before`, `let`, etc). (RSpec::Core::ExampleGroup::WrongScopeError)

Not only for this example but other times, I don't fully understand what the allowable scope is for let and for creating instances in Rspec.

What's the use case of let here versus just me creating using schedule = blah blah?

I guess I understand the literal intent of the error: I cannot use schedule in context only in it. But what's the right way then with this example to put stuff under describe, context, or it and in what way?

Answer 1

Let is lazily evaluated which is nice when you want to share a variable across tests but only when the test needs it.

From the docs:

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.

You're getting a method missing here because of this line:

schedule.create_recurring_event('test-keyword', 'slack', 'day', '10 AM') 

It seems you want that line to be evaluated before each it block in that context. You would just rewrite it like so:

describe "#check_recurring_and_send_message" do
  let(:schedule) {ScheduleKaya.new('test-client-id')}
  context "when it is 11AM and recurring event time is 10AM" do
    before(:each) do
      schedule.create_recurring_event('test-keyword', 'slack', 'day', '10 AM')
    end
    it "sends an SMS" do
    end
    it "set the next_occurrence to be for 10AM tomorrow" do
      tomorrow = Chronic.parse("tomorrow at 10AM")
      expect(schedule.next_occurrence).to eq(tomorrow)
    end
  end
end