def at_exit(&block)
      return proc {} unless running || block_given?
      @at_exit = block if block_given?
      @at_exit ||= proc { SimpleCov.result.format! }
    end
def at_exit(&block)
      return proc {} unless running || block_given?
      @at_exit = block if block_given?
      @at_exit ||= proc { SimpleCov.result.format! }
    end
Gets or sets the behavior to process coverage results.

 By default, it will call SimpleCov.result.format!

 Configure with:

     SimpleCov.at_exit do
       puts "Coverage done"
       SimpleCov.result.format!
     end