RSpec Magic Part 1: Lets

When I first started to use RSpec one of the tricks I was shown was how to extract the set up for each test into a ‘let’. It looks something like this:

let(:variable_name) { statement }

So we can transform a variable declaration in a test block that looks like this:

bicycle = Bicycle.new

into something more generic that lives in the describe block:

let(:bicycle) { Bicycle.new }

And that’s exactly how I used it from there on. You can even do the neat trick of declaring doubles in a let, along with method stubs:

let(:broken_bicycle) { double :bicycle, broken?: :true }

But let’s try and see what’s going on here. We have a method let, which takes a symbol as an argument, and then takes a block which it assigns to that symbol, converted to a variable. Another way of writing this, just to make it explicit:

let(:bicycle) do
    Bicycle.new
end