public void Test_POP(byte opcode)
        {
            ushort sp      = 0x4242;
            byte   lsbData = 0xFF;
            byte   msbData = 0x11;

            var expectedState = new CpuState();

            expectedState.StackPointer = (ushort)(sp + 2);

            switch (opcode)
            {
            case 0xC1:
                expectedState.Registers.BC = (ushort)((msbData << 8) | lsbData);
                break;

            case 0xD1:
                expectedState.Registers.DE = (ushort)((msbData << 8) | lsbData);
                break;

            case 0xE1:
                expectedState.Registers.HL = (ushort)((msbData << 8) | lsbData);
                break;

            case 0xF1:
                expectedState.Registers.F = lsbData;
                expectedState.Registers.A = msbData;
                break;
            }

            var actualState = new CpuState();

            actualState.StackPointer = sp;

            var memoryMock = new Mock <IRandomAccessMemory>();

            memoryMock.Setup(m => m.ReadByte(sp)).Returns(lsbData);
            memoryMock.Setup(m => m.ReadByte((ushort)(sp + 1))).Returns(msbData);

            var instruction = new POP();

            instruction.Initialize(opcode);

            //act
            while (!instruction.IsFetchNecessary())
            {
                instruction.ExecuteCycle(actualState, memoryMock.Object);
            }

            //assert
            TestHelper.AssertCpuState(expectedState, actualState);
            memoryMock.Verify(m => m.WriteByte(It.IsAny <ushort>(), It.IsAny <byte>()), Times.Never);
        }