UnitTestExample.java

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

import static junit.framework.TestCase.assertEquals;
import static junit.framework.TestCase.fail;

public class UnitTestExample {
    private UnitUnderTest unit;
    @Before
    public void setup() {
        //Recreate instance before evert @Test to get it in a known state
        unit = new UnitUnderTest();
    }

    @Test
    public void testIntFoo() {
        Assert.assertEquals(42, unit.intFoo());
    }

    @Test
    public void testStringFoo() {
        Assert.assertEquals("42", unit.stringFoo());
    }

    @Test
    public void testIntBar() {
        int value = unit.intBar();
        if(value < 1 || value > 6) {
            fail("Invalid value: " + value);
        }
    }

    @Test
    public void testStringBar() {
        int value = Integer.parseInt(unit.stringBar());
        if(value < 1 || value > 6) {
            fail("Invalid value: " + value);
        }
    }

    @Test
    public void testMult() {
        assertEquals(2, unit.mult(1, 2));
        assertEquals(2, unit.mult(2, 1));
        assertEquals(10, unit.mult(2, 5));
        assertEquals(-10, unit.mult(-2, 5));
    }
}

UnitUnderTest.java

import java.util.Random;

public class UnitUnderTest {
    private Random random = new Random();

    public int intFoo() {
        return 42;
    }

    public String stringFoo() {
        return Integer.toString(intFoo());
    }

    public int intBar() {
        return random.nextInt(6) + 1;//Throw dice
    }

    public String stringBar() {
        return Integer.toString(intBar());
    }

    public int mult(int input, int factor) {
        return input * factor;
    }
}