Ruby: How to use global variables for a conditional debugger

You can share a state in Ruby with global variables Show archive.org snapshot . Even if you should avoid them whenever possible, for debugging an application this could be temporary quite handy.

Example:

class User

  after_save { byebug if $debug; nil }

  def lock
   self.locked = true
   save
  end

end

Rspec.describe User do

  let(:user) { create(:user) } 

  before do
   # Many users are created and saved in this hook, but we don't want the debugger to stop for them
   10.times { create(:user) }
  end

  it do
    # At this point we want to stop in the debugger for all following tests, when the :lock call runs into the after_save
    $debug = true
    expect { user.lock }.to change(user, :locked).from(false).to(true) 
  end

end

Running this spec will only trigger one debug session. Otherwise you will have to count how many times you exited the debug session to ensure you are in the "desired" session.