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

I like @jon-rowe's solution (no additional gems needed) with a slight edit: I really don't care about other errors as much as RSpec::Expectations::ExpectationNotMetError.

  config.around(:each) do |example|
    example.run.tap do |result|
      debugger if result.is_a?(RSpec::Expectations::ExpectationNotMetError)
    end
  end

Answer 2

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

Answer 3

You can use plymouth gem https://github.com/banister/plymouth for that. It is using pry though, a (better) alternative to irb.

HTH

Answer 4

Use pry-rescue, it's the spiritual successor to plymouth:

From the Readme:

If you're using RSpec or respec, you can open a pry session on every test failure using rescue rspec or rescue respec:

$ rescue rspec
From: /home/conrad/0/ruby/pry-rescue/examples/example_spec.rb @ line 9 :

     6:
     7: describe "Float" do
     8:   it "should be able to add" do
 =>  9:     (0.1 + 0.2).should == 0.3
    10:   end
    11: end

RSpec::Expectations::ExpectationNotMetError: expected: 0.3
     got: 0.30000000000000004 (using ==)
[1] pry(main)>

Answer 5

You won't get access to local variables (easily) without debugger being in scope of the block, however RSpec provides you with around hooks which let's you do this:

config.around(:each) do |example|
  result = example.run
  debugger if result.is_a?(Exception)
  puts "Debugging enabled"
end

You then have access to @ivars and subject / let(:var) contents at this point.

Answer 6

You can try hammertime. It will stop and prompt to take you into an interactive debugging session whenever an exception is raised.