You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: registers_saving_buffer_test.rb
    path of file: ./repos/tenderjit/test
    
    the code of the file until where you have to start completion: require "helper"

class TenderJIT
  class RegistersSavingBufferTest < Test
    def prepare_buffer
      fisk = Fisk.new

      buffer = RegistersSavingBuffer.new Fisk::Helpers.mmap_jit(4096), 4096

      fisk.asm(buffer) do
        # Avoid messing with RSP/R
    
    def test_saving
      buffer = prepare_buffer

      buffer.to_function([], Fiddle::TYPE_VOID).call

      assert_equal buffer.saved_rax, 0x02_03_04_05
      assert_equal buffer.saved_rbx, 0x03_04_05_06
      assert_equal buffer.saved_rcx, 0x04_05_06_07
      assert_equal buffer.saved_rdx, 0x05_06_07_08
      assert_equal buffer.saved_rsi, 0x06_07_08_09
      assert_equal buffer.saved_rdi, 0x07_08_09_10
      assert_equal buffer.saved_r8,  0x09_10_11_12
      assert_equal buffer.saved_r9,  0x10_11_12_13
      assert_equal buffer.saved_r10, 0x11_12_13_14
      assert_equal buffer.saved_r11, 0x12_13_14_15
      assert_equal buffer.saved_r12, 0x13_14_15_16
      assert_equal buffer.saved_r13, 0x14_12_10_08
      assert_equal buffer.saved_r14, 0x15_13_11_09
      assert_equal buffer.saved_r15, 0xde_ad_ca_fe
    end