method BadNbr$($a: array$)$ returns $($bn: int$)$

$\{$

$//$ If array is empty or has only one element, return $-1$ as there are no valid neighbors

$$ if a$.$Length $==0||$ a$.$Length $==1\{$

$$ return $-1$;

$\}$

$//$ Loop through each element to find the first bad neighbor

$$ for i :$=0$ to a$.$Length $-1\{$

$//$ Determine the index of the right neighbor, with wrap$-$around

$$ var rightIndex :$=($i $+1)\%$ a$.$Length;

$//$ Check if the sum of the element and its right neighbor is negative

$$ if a$[$i$]+$ a$[$rightIndex$]<mtext></mtext><mn>0</mn><mtext></mtext><mi>\{</mi>$

$$ return rightIndex; $//$ Return the index of the first bad neighbor found

$\}$

$\}$

$//$ If no bad neighbor was found, return $-1$

$$ return $-1$;

$\}$

$//$ Test function to validate the BadNbr method with various test cases

method TestBadNbr$()$

$\{$

$$ var a$1$ :$=$ new int$[2]$;

$$ a$1[0],$ a$1[1]$ :$=0,-1$;

$$ assert a$1[0]==0$;

$$ assert a$1[1]==-1$;

$$ var result$1$ :$=$ BadNbr$($a$1)$;

$$ assert result$1==0$;

ex$1.$dfy$(31,11)$: Error: assertion might not hold

$31|$ assert result$1==0$;

Dafny program verifier finished with $1$ verified, $1$ error

$($Q$)$

It seems that the current postcondition in your Dafny code is too weak to pass all the test cases. Consider adding a more robust postcondition to ensure that all test cases pass successfully. Please keep the following guidelines in mind:

Requirements:

Use camelCase for method names, and only use lowercase for functions, predicates, and filenames.

Ensure that all your solutions verify without any warnings or errors using Dafny version $4\mathrm{.}7.$