Custom formatters

RSpec ships with general purpose output formatters. You can tell RSpec which one to use using the --format command line option.

When RSpec’s built-in output formatters don’t, however, give you everything you need, you can write your own custom formatter and tell RSpec to use that one instead. The simplest way is to subclass RSpec’s BaseTextFormatter, and then override just the methods that you want to modify.

Custom formatter

Given a file named “custom_formatter.rb” with:

class CustomFormatter
  # This registers the notifications this formatter supports, and tells
  # us that this was written against the RSpec 3.x formatter API.
  RSpec::Core::Formatters.register self, :example_started

  def initialize(output)
    @output = output

  def example_started(notification)
    @output << "example: " << notification.example.description

And a file named “example_spec.rb” with:

RSpec.describe "my group" do
  specify "my example" do

When I run rspec example_spec.rb --require ./custom_formatter.rb --format CustomFormatter

Then the output should contain “example: my example”

And the exit status should be 0.