Sane guidelines for setting up Rspec tests with subject, let, and before(:each)

subject_let_and_before.txt

1. subject:

Use subject for creating the subject. Named subjects should be preferred unless
used only implicitly thereafter

i.e.: 

subject(:user) { create(:user) }

where "user.bar" will be preferred over "subject.bar"

2. let:

Use let and let! for non-subject vars or objects needed. 
let is lazy, memoized, and local. Three wins

3. before:

Use before(:each) for methods or complex setups that require methods. 
Or only use before when subject and let are not enough.
Beware of before(:all): avoid it unless you know why and where.

4. Consider writing your own helper methods for very complex setup. 
However, if setup is complex, this can be an indication that design of 
classes to be tested is too complicated and should be simplified.

Examples:

Here is an example complex set up from VCR specs that uses subject, let, and before:

subject { HooksClass.new }
  let(:invocations) { [] }

  before(:each) do
    subject.instance_eval do
      define_hook :before_foo
      define_hook :before_bar
    end
  end


Here is an example that creates test doubles (mocks) in a context using let:


describe Transfer do
  context "transfer with amount of 10" do
    let(:source_account) { double :source_account, :decrease => nil }
    let(:destination_account) { double :destination_account, :increase => nil }