How to write a Tester in java?

I have a school project due next week and I'm trying to crack the way to solve this question. I need to develop a program (tester) for the code written below, which had to print the 2 smallest numbers out of 4 using if-switch. The numbers they want me to use are 0,1.

if (a > b) {

    int tmp = b;
    b = a;
    a = tmp;
}

if (b > c) {
    int tmp = c;
    c = b;
    b = tmp;
}

if (a > d) {
    int tmp = d;
    d = a;
    a = tmp;
}

if (b > d) {
    int tmp = d;
    d = b;
    b = tmp;
}

My limitations are:

Must only use: int, for, while, if, Scanner (so no break, array, Boolean, etc.) No user input, must enter to test a, d = 0 c, b = 1. I know there are 16 options, if all are true, then print verified, in any case there must be written in the tester a code that prints 1 example if false. I'm trying to solve this with for statements, however I only got as far as just printing 1 + 2, 3 + 4, ... in: for (int i = 0; i <= 16; i++).

How do I check the numbers they want for the test for the code above (0,1) over and over in for loop? I would appreciate a hint on printing just 1 example for the false print