Testing for "bouncy" numbers
The use of magic numbers isn't great.  Your xTest functions should really have Boolean return values, which would allow you to remove the local storage of the result and simplify further (relying on operator short-circuiting):

void testNumber(int number) {
    if (sameDigitsTest(number) || decreasingTest(number) || increasingTest(number)) {
        nonBouncyCounter++;
    }
    else if (bouncyTest(number)) {
        bouncyCounter++;
    }
}


(Note that the latter does actually work with the current int return values, but it appears that you've only coded them that way to fit your original implementation; it's unnecessary complexity.)