Stub methods like Rspec

Could you recognise what is it doing next code?

let(:fran_user) { User.new }

before do
 allow(fran_user).to receive(:nickname).and_return("martinezcoder")
end

it { expect(fran_user.hi).to return("Hi, this is martinezcoder!")}

Sure! This is a call to stub a method with Rspec. But,

• Could you do the same without using Rspec?
• Do you know how to stub the method of a single instance?

In this case, considering that fran_user is an instance of User, I am suposse to have a User class including the method hi and nickname. When running the test, if the instance fran_user uses the method hi, it will respond “Hi, this is martinezcoder!”, instead of the returned value defined in the method.

class User
  def nickname
    "me"
  end

  def hi
    "Hi, this is #{nickname}!"
  end
end

fran_user = User.new
puts fran_user.hi

Last code will puts:

=> "Hi, this is me!"

How to stub the instance of User without using Rspec?

Stub the nickname method of the fran_user instance:

fran_user = User.new
puts fran_user.hi

class << fran_user
  def nickname
    "martinezcoder"
  end
end

puts fran_user.hi

Last code will puts:

=> "Hi, this is me!"
=> "Hi, this is martinezcoder!"

So you now know how to stub an instance method without the dependency of Rspec!