Incrementor.java

public class Incrementor {
    /**
     * The current number
     */
    private int number = 0;

    /**
     * The maximum value that number can be
     */
    private int max = Integer.MAX_VALUE;

    /**
     * The method that increments current number
     */
    public void incrementNumber() {
        number++;
        if (number == max) {
            number = 0;
        }
    }

    /**
     * @return Current Maximum for number
     */
    public int getMax() {
        return max;
    }

    /**
     * <p>The method that set the maximum value for number
     *
     * @param max the value that will set as maximum value
     */
    public void setMax(int max) {
        try {
            if (max >= 0) {
                this.max = max;
                if (number > max) {
                    number = 0;
                }
            } else {
                throw new Exception("Maximum value cannot be lower than number");
            }
        } catch (Exception e){}
    }

    /**
     * @return Current number
     */
    public int getNumber() {
        return number;
    }
}

IncrementorUnitTest.java

import org.junit.Assert;
import org.junit.Test;

import static org.junit.Assert.assertEquals;

/**
 * Unit Test for Incrementor
 */
public class ExampleUnitTest {

    @Test
    public void increment() {
        Incrementor incrementor = new Incrementor();
        incrementor.incrementNumber();
        incrementor.incrementNumber();
        incrementor.incrementNumber();

        assertEquals(3, incrementor.getNumber());

    }


    @Test
    public void setMaximum() {
        Incrementor incrementor = new Incrementor();
        try {
            incrementor.setMax(10);
        } catch (Exception e) {
            assertEquals("Maximum value cannot be lower than number", e.getMessage());
        }
        assertEquals(10, incrementor.getMax());
    }

    @Test
    public void setNegativeMaximum() {
        Incrementor incrementor = new Incrementor();
        try {
            incrementor.setMax(-10);
            Assert.fail("Expected exception");
        } catch (Exception e) {
            assertEquals("Maximum value cannot be lower than number", e.getMessage());
        }
    }

    @Test
    public void incrementNumberWithMaximum() {
        Incrementor incrementor = new Incrementor();

        try {
            incrementor.setMax(10);
            for (int i = 0; i < 10; i++) {
                incrementor.incrementNumber();
            }
            assertEquals(0, incrementor.getNumber());
        } catch (Exception e) {
            Assert.fail(e.getMessage());
        }

    }
}