Rspec matcher to check if input is JSON.

should_be_json.rb

RSpec::Matchers.define :be_json do
  match do |actual|
    begin
      !!JSON.parse(actual)
    rescue
      false
    end
  end

  failure_message_for_should do |actual|
    "expected input to be JSON"
  end

  failure_message_for_should_not do |actual|
    "expected input not to be JSON"
  end

  description do
    "checks if input is JSON"
  end
end