How would you create a test program for the following Java code? $```$

import java.math.BigDecimal;

import java.math.RoundingMode;

import java.util.HashMap;

public class Calculator $\{$

private BigDecimal RX;

private BigDecimal RY;

private BigDecimal RM;

private BigDecimal RZ;

private HashMap registers;

public Calculator$()\{$

RX $=$ BigDecimal.ZERO;

RY $=$ BigDecimal.ZERO;

RM $=$ BigDecimal.ZERO;

RZ $=$ BigDecimal.ZERO;

registers $=$ new HashMap;

registers.put$("$RX$",$ RX$)$;

registers.put$("$RY$",$ RY$)$;

registers.put$("$RM$",$ RM$)$;

registers.put$("$RZ$",$ RZ$)$;

$\}$

public String parseInput$($String input$)\{$

String$[]$ tokens $=$ input.split$("")$;

String command $=$ tokens$[0].$toLowerCase$()$;

if $($command$.$equals$("$mov$"))\{$

return movCommand$($tokens$)$;

$\}$ else if $($command$.$equals$("$add$"))\{$

addCommand$()$;

return null;

$\}$ else if $($command$.$equals$("$mul$"))\{$

mulCommand$()$;

return null;

$\}$ else if $($command$.$equals$("$div$"))\{$

divCommand$()$;

return null;

$\}$ else if $($command$.$equals$("$sub$"))\{$

subCommand$()$;

return null;

$\}$ else if $($command$.$equals$("$sho$"))\{$

return shoCommand$($tokens$)$;

$\}$ else if $($command$.$equals$("$clr$"))\{$

return clrCommand$($tokens$)$;

$\}$ else if $($command$.$equals$("$zmm$"))\{$

zmmCommand$()$;

return null;

$\}$ else if $($command$.$equals$("$mem$"))\{$

return memCommand$($tokens$)$;

$\}$ else $\{$

return "Error: Invalid command";

$\}$

$\}$

$``````$

private String movCommand$($String$[]$ tokens$)\{$

if $($tokens$.$length $!=4||!$tokens$[2].$equals$(","))\{$

return "ERROR: Invalid command";

$\}$

BigDecimal value;

try $\{$

value $=$ new BigDecimal$($tokens$[1])$;

$\}$ catch $($NumberFormatException e$)\{$

return "ERROR: Invalid value";

$\}$

String register $=$ tokens$[3].$toUpperCase$()$;

if $($register$.$equals$("$RX$")||$ register.equals$("$RY$")||$ register.equals$("$RM$"))\{$

registers.put$($register$,$ value$)$;

return null;

$\}$ else $\{$

return "Error: Invalid register";

$\}$

$\}$

private void addCommand$()\{$

RZ $=$ RX$.$add$($RY$)$;

$\}$

private void mulCommand$()\{$

RZ $=$ RX$.$multiply$($RY$)$;

$\}$

private void divCommand$()\{$

RZ $=$ RX$.$divide$($RY$,20,$ RoundingMode.CEILING$)$;

$\}$

private void subCommand$()\{$

RZ $=$ RX$.$subtract$($RY$)$;$|$

$\}$

private String shoCommand$($String$[]$ tokens$)\{$

if $($tokens$.$length $!=2)\{$

return "Error: Invalid command";

$\}$

String register $=$ tokens$[1].$toUpperCase$()$;

if $($registers$.$containsKey$($register$))\{$

return registers.get$($register$).$toString$()$;

$\}$ else $\{$

return "Error: Invalid register";

$\}$

$\}$

private String clrCommand$($String$[]$ tokens$)\{$

if $($tokens$.$length $!=2)\{$

return "Error: Invalid command";

$\}$

String register $=$ tokens$[1].$toUpperCase$()$;

if $($registers$.$containsKey$($register$))\{$

registers.put$($register$,$ BigDecimal.ZERO$)$;

return null;

$\}$ else $\{$

return "Error: Invalid register";

$\}$

$\}$

$``````$

private String memCommand$($String$[]$ tokens$)\{$

if $($tokens$.$length $!=2)\{$

return "Error: Invalid command";

$\}$

String register $=$ tokens$[1].$toUpperCase$()$;

if $($register$.$equals$("$RX$")||$ register.equals$("$RY$"))\{$

registers.put$($register$,$ RM$)$;

return null;

$\}$ else $\{$

return "Error: Invalid register";

$\}$

$\}$

$\}$

$```$