$/**$

$*$ Checks array to see if it is a Fibonacci sequence

$*$

$*$ @param x array to check

$*$ @return true if it is fibonacci and false otherwise

$*$ @throws NullPointerException if x is null

$*/$

public static boolean isFibonacciSeries$($int$[]$ x$)\{$

if $($x$.$length $<2)\{$

return false;

$\}$

for $($int i $=2$; i $<$ x$.$length; i$++)\{$

if $($x$[$i$]!=$ x$[$i $-1]+$ x$[$i $-2])\{$

return false;

$\}$

$\}$

return true;

$\}$

a$.$ What is the fault in the code above? Describe it precisely

b$.$ If possible, give a test case that does not execute the fault. If not possible, explain why it is not possible

c$.$ If possible, give a test case that executes the fault, but does not result in an error state. If not possible, explain why it is not possible

d$.$ If possible, give a test case that results in an error state but not in failure. If not possible, explain why it is not possible

e$.$ Provide a repair to the code to fix the fault