Start ruby debugger if rspec test fails

Question

Often, when a test fails, I spend quite sometime trying to figure out the what caused it to fail. It\'d be useful if RSpec could kick off a Ruby debugger when the test fails, so

Answer 1

You need to catch the ExpectationNotMatched exception while it's being constructed. Include the following code in your helpers somewhere and RSpec will stop when the exception is being constructed. This will be several levels deep inside the matchers, so in the debugger, say "where" then "up 5"or "up 6" and you'll be inside the instance_exec of your block. The debugger doesn't show the code correctly in the version I'm using, but you can "up" one more time and get to code running in the same context where your test is evaluated, so you can inspect the instance variables (but not local variables, it seems).

require 'debugger'
require 'rspec'

Debugger.start
class RSpec::Expectations::ExpectationNotMetError
  alias_method :firstaid_initialize, :initialize

  def initialize *args, &b
    send(:firstaid_initialize, *args, &b)
    puts "Stopped due to #{self.class}: #{message} at "+caller*"\n\t"
    debugger
    true # Exception thrown
  end
end

describe "RSpec" do
  it "should load use exceptions on should failure" do
    @foo = :bar    # An instance variable I can examine
    1.should == 2
  end
end