Computing with Data

elgeish

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Previous: Dealing with Randomness - Part I Next: Test Case Anatomy - Part I

Dealing with Randomness - Part II

we can set the seed of the random number generator so that each time the test case runs it's predictable instead of pseudo-random; here's an example:

import com.google.common.annotations.VisibleForTesting;
import org.testng.annotations.Test;
import java.util.Random;
import static org.testng.Assert.*;
class CoinFlipper {
  public enum Face {HEAD, TAIL}
  
  private Random random = new Random();
  
  public Face flip() {
    return random.nextBoolean() ? Face.HEAD : Face.TAIL;
  }
  
  @VisibleForTesting
  void setRandom(final Random random) {
    this.random = random;
  }
}
public class CoinFlipperTest {
  @Test
  public void testFlip() {
    final CoinFlipper flipper = new CoinFlipper();
    final Random random = new Random(42);
    
    flipper.setRandom(random);
    assertEquals(flipper.flip(), CoinFlipper.Face.HEAD);
    assertEquals(flipper.flip(), CoinFlipper.Face.TAIL);
    assertEquals(flipper.flip(), CoinFlipper.Face.HEAD);
  }
}

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272/300 Dealing with Randomness - Part II

Dealing with Randomness - Part II

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