testing methods for Semi-MagicSquare

I want to use the command "java MagicSquare -t" to test the four following methods which are testIsFullSolution, testRject, testExtend, testNext:

-testIsFullSolution, a method that generates partial solutions and ensures that
the isFullSolution method correctly determines whether each is a complete
solution.

-testReject, a method that generates partial solutions and ensures that the reject method correctly determines whether each should be rejected.

-testExtend, a method that generates partial solutions and ensures that the
extend method correctly extends each with the correct next choice.

-testNext, a method that generates partial solutions and ensures that the, in
each, next method correctly changes the most recent choice that was added to
its next option.

I can successfully compile the program but when I run it, I got the following:

These should be full:
Full sol'n: [[8, 1, 6], [3, 5, 7], [4, 9, 2]]

These should NOT be full:
Full sol'n: [[8, 1, 6], [3, 5, 7], [4, 9, 0]]

These should NOT be rejected:
Not rejected:   [[I@7f31245a, [I@6d6f6e28, [I@135fbaa4]

These should be rejected:
Not rejected:   [[I@45ee12a7, [I@330bedb4, [I@2503dbd3]

These can NOT be extended:

Exception in thread "main" java.lang.NegativeArraySizeException
at cs445.a3.MagicSquare.extend(MagicSquare.java:111)
at cs445.a3.MagicSquare.testExtend(MagicSquare.java:236)
at cs445.a3.MagicSquare.main(MagicSquare.java:335)

And here is part of my code:

static void testIsFullSolution() {
    int[][] fullSolutions = new int[][] {
        {8, 1, 6},
        {3, 5, 7},
        {4, 9, 2},
    };

    int[][] notFullSolutions = new int[][] {
        {8, 1, 6},
        {3, 5, 7},
        {4, 9, 0},
    };

    System.err.println("These should be full:");
    if (isFullSolution(fullSolutions)) {
        System.err.println("\tFull sol'n:\t" + Arrays.deepToString(fullSolutions));
    } else {
        System.err.println("\tNot full sol'n:\t" + Arrays.deepToString(fullSolutions));
    }

    System.err.println("These should NOT be full:");
    if (isFullSolution(notFullSolutions)) {
        System.err.println("\tFull sol'n:\t" + Arrays.deepToString(notFullSolutions));
    } else {
        System.err.println("\tNot full sol'n:\t" + Arrays.deepToString(notFullSolutions));
    }


}

static void testReject() { 
    int[][] notRejected = new int[][] {
        {8, 1, 6},
        {3, 5, 7},
        {4, 9, 2},
    };

    int[][] rejected = new int[][] {
         {2, 0, 0},
         {0, 4, 0},
         {0, 0, 6},
    };
     System.err.println("These should NOT be rejected:");
     if (reject(notRejected)) {
         System.err.println("\tRejected:\t" + Arrays.toString(notRejected));
     } else {
         System.err.println("\tNot rejected:\t" + Arrays.toString(notRejected));
     }

     System.err.println("These should be rejected:");
     if (reject(rejected)) {
         System.err.println("\tRejected:\t" + Arrays.toString(rejected));
     } else {
         System.err.println("\tNot rejected:\t" + Arrays.toString(rejected));
     }

static void testExtend() {
     int [][] noExtend = new int [][] {
        {8,1,6},
        {3,5,7},
        {4,9,2},
    };

    int [][] extend = new int [][] {
        {8,1,6},
        {3,5,7},
        {4,9,0},
    };

    System.err.println("These can NOT be extended:");
    System.err.println("\tExtended " + Arrays.toString(noExtend) + " to " + Arrays.toString(extend(noExtend)));

    System.err.println("These can be extended:");
    System.err.println("\tExtended " + Arrays.toString(extend) + " to " + Arrays.toString(extend));

}

static void testNext() {
    int [][] noNext = new int [][] {
        {8,1,6},
        {3,5,7},
        {4,9,2},
    };

    int [][] next = new int [][] {
        {8,1,6},
        {3,5,7},
        {4,9,0},
    };

    System.err.println("These can NOT be next'd:");
    System.err.println("\tNexted " + Arrays.toString(noNext) + " to " + Arrays.deepToString(next(noNext)));

    System.err.println("These can be next'd:");
    System.err.println("\tNexted " + Arrays.toString(next) + " to " + Arrays.deepToString(next(next)));

}

 public static void main(String[] args) {
    if (args.length >= 1 && args[0].equals("-t")) {
        System.out.println("Running tests...");
        testIsFullSolution();
        testReject();
        testExtend();
        testNext();
    } else if (args.length >= 2) {
        try {
            // First get the specified size
            size = Integer.parseInt(args[0]);
            // Then read the square from the file
            int[][] square = readSquare(args[1]);

            System.out.println("Starting square:");
            printSquare(square);

            findBack(square);

            System.out.println("\nSolution:");
            printSquare(solve(square));
        } catch (NumberFormatException e) {
            // This happens if the first argument isn't an int
            System.err.println("First argument must be size");
        } catch (FileNotFoundException e) {
            // This happens if the second argument isn't an existing file
            System.err.println("File " + args[1] + " not found");
        }
    } else if (args.length >= 1) {
        try {
            // First get the specified size
            size = Integer.parseInt(args[0]);
            // Then initialize to a blank square
            int[][] square = new int[size][size];

            System.out.println("Starting square:");
            printSquare(square);

            findBack(square);

            System.out.println("\nSolution:");
            printSquare(solve(square));
        } catch (NumberFormatException e) {
            // This happens if the first argument isn't an int
            System.err.println("First argument must be size");
        }
    } else {
        System.err.println("See usage in assignment description");
    }
}

public static int[][] extend(int[][] square) {
    // TODO: Complete this method
    int[][] temp;
    boolean getFlag = false;
    temp = new int[size][size];
    for (int i = 0; i < size; i++){
        for (int j = 0; j < size; j++){
            if (square[i][j] == 0 && !getFlag){
                temp[i][j] = 1;
                getFlag = true;
            }
            else{
                temp[i][j] = square[i][j];
            }
        }
    }
    if (getFlag){
        return temp;
    }
    else{
        return null;
    }   
}