Q quick test to show how MiniTest let works. The let block is reevaluated for everytime, so it is basically the same as before but lazily evaluated whereas before is executed always even if none of the results are used for a test.

let_test.rb

require 'rubygems'
require 'minitest/autorun'

describe 'let_test' do
  
  let(:sub) { 
    puts "   - lazy :sub called"
    true
  }
  
  it("is empty") { 
    puts "=== call 1.1"
    sub.must_equal true
    puts "=== call 1.2"
    sub.must_equal true
    puts "=== call 1.3"
    sub.must_equal true
  }
  
  it("is filled") { 
    puts "=== call 2.1"
    sub.must_equal true
    puts "=== call 2.2"
    sub.must_equal true
    puts "=== call 2.3"
    sub.must_equal true
  }
  
end

The result of ruby let_test.rb is:

$ ruby let_test.rb 
Run options: --seed 57795

# Running tests:

=== call 1.1
   - lazy :sub called
=== call 1.2
=== call 1.3
.=== call 2.1
   - lazy :sub called
=== call 2.2
=== call 2.3
.

Finished tests in 0.000939s, 2129.9255 tests/s, 6389.7764 assertions/s.

2 tests, 6 assertions, 0 failures, 0 errors, 0 skips