app.rb

module TraceCalls
	def self.included(klass)
		def klass.method_added(method)
			return if @_meta_yo
			@_meta_yo = true
			alias_method :"#{method} old", method
			define_method(method) do |*args|
				puts "--> Calling #{method} with #{args.inspect}"
				out = send(:"#{method} old", *args)
				puts "<-- Returned #{out.inspect}"
				out
			end
			@_meta_yo = false
		end
	end
end

class Test
	include TraceCalls

	def test(a)
		a
	end

	def calc(a, b)
		a + b
	end
end

test = Test.new
puts test.test('asd')
puts test.calc(5, 6)

output

: voldern@harry ~/Kode/ruby/lek > ruby trace.rb
--> Calling test with ["asd"]
<-- Returned "asd"
asd
--> Calling calc with [5, 6]
<-- Returned 11
11