How can I validate exits and aborts in RSpec?

Question

I am trying to spec behaviors for command line arguments my script receives to ensure that all validation passes. Some of my command line arguments will result in abort or exit being invoked because the parameters supplied are missing or incorrect.

I am trying something like this which isn't working:

# something_spec.rb
require 'something'
describe Something do
    before do
        Kernel.stub!(:exit)
    end

    it "should exit cleanly when -h is used" do
        s = Something.new
        Kernel.should_receive(:exit)
        s.process_arguments(["-h"])
    end
end

The exit method is firing cleanly preventing RSpec from validating the test (I get "SystemExit: exit").

I have also tried to mock(Kernel) but that too is not working as I'd like (I don't see any discernible difference, but that's likely because I'm not sure how exactly to mock Kernel and make sure the mocked Kernel is used in my Something class).

Answer 1

After digging, I found this.

My solution ended up looking like this:

# something.rb
class Something
    def initialize(kernel=Kernel)
        @kernel = kernel
    end

    def process_arguments(args)
        @kernel.exit
    end
end

# something_spec.rb
require 'something'
describe Something do
    before :each do
        @mock_kernel = mock(Kernel)
        @mock_kernel.stub!(:exit)
    end

    it "should exit cleanly" do
        s = Something.new(@mock_kernel)
        @mock_kernel.should_receive(:exit)
        s.process_arguments(["-h"])
    end
end

Answer 2

try this:

module MyGem
  describe "CLI" do
    context "execute" do

      it "should exit cleanly when -h is used" do
        argv=["-h"]
        out = StringIO.new
        lambda { ::MyGem::CLI.execute( out, argv) }.should raise_error SystemExit
      end

    end
  end
end

Answer 3

Thanks for the answer Markus. Once I had this clue I could put together a nice matcher for future use.

it "should exit cleanly when -h is used" do
  lambda { ::MyGem::CLI.execute( StringIO.new, ["-h"]) }.should exit_with_code(0)
end
it "should exit with error on unknown option" do
  lambda { ::MyGem::CLI.execute( StringIO.new, ["--bad-option"]) }.should exit_with_code(-1)
end

To use this matcher add this to your libraries or spec-helpers:

module ExitCodeMatchers
  Spec::Matchers.define :exit_with_code do |code|
    actual = nil
    match do |block|
      begin
        block.call
      rescue SystemExit => e
        actual = e.status
      end
      actual and actual == code
    end
    failure_message_for_should do |block|
      "expected block to call exit(#{code}) but exit" +
        (actual.nil? ? " not called" : "(#{actual}) was called")
    end
    failure_message_for_should_not do |block|
      "expected block not to call exit(#{code})"
    end
    description do
      "expect block to call exit(#{code})"
    end    
  end  
end

Spec::Runner.configure do |config|
  config.include(ExitCodeMatchers)
end