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Previous: Test Hooks - Part II Next: Dealing with Randomness - Part II

Dealing with Randomness - Part I

Here's an example of a Java unit test that verifies the behavior of a coin-flipping Bernoulli trial:

import org.testng.annotations.Test;
import java.util.Random;
import static org.testng.Assert.*;
class CoinFlipper {
public enum Face {HEAD, TAIL}
private final Random random = new Random();
public Face flip() {
return random.nextBoolean() ? Face.HEAD : Face.TAIL;
public class CoinFlipperTest {
public void testFlip() {
final CoinFlipper flipper = new CoinFlipper();
final int trialsCount = 100;
int headsCount = 0;
for (int i = 0; i < trialsCount; i++) {
if (flipper.flip() == CoinFlipper.Face.HEAD) {
assertTrue(Math.abs(headsCount - trialsCount / 2) <= 5);
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