Using let instance of instance variables in minitest.

foo_test.rb

# Using instance variables
describe "Foo" do   
  before do     
    @foo = FactoryGirl.create :foo   
    @bar = FactoryGirl.create :bar     
  end      

  it "sends message" do     
    assert @foo.msg("pow!")
    # @bar is not used in this test
  end

  it "sends bar" do     
    assert @foo.msg(@bar)
  end

end 

# Using let
describe "Foo" do   
  let(:foo) { FactoryGirl.create :foo }
  let(:bar) { FactoryGirl.create :bar }

  it "sends message" do     
    assert foo.msg("pow!")
    # bar is not used in this test, but it's not instantiated so all is good
  end

  it "sends bar" do     
    assert foo.msg(bar)
  end

end 

# Note, "let" is just a memoized method. Like the rest of Minitest it's pretty simple.
# These are equivalent:

let(:foo) { FactoryGirl.create :foo }

def foo do
  @_memoized ||= {}
  @_memoized.fetch(:foo) {|k| @_memoized[k] = FactoryGirl.create :foo }
end