Why Is Unit Testing So Hard? - Example 2

example-2_source_why-is-unit-testing-so-hard.cs

public class Powerup : IPowerup
{
  public double Multiplier { get; }
}

public class Player
{
  private const int MaxPowerups = 4;
  
  private Weapon _weapon;
  
  public List<IPowerup> Powerups { get; } = new List<IPowerup>();
  
  public double Damage => _weapon.Damage * Powerups.Take(MaxPowerups).Sum(p => p.Multiplier);
}

example-2_tests_why-is-unit-testing-so-hard.cs

public class PlayerTest
{
  [Test]
  public void OnePowerupDamage()
  {
    var weapon = Substitute.For<Weapon>();
    weapon.Damage.Returns(1);
    var powerup = Substitute.For<IPowerup>();
    powerup.Multiplier.Returns(2);
    var player = new Player(weapon);
    
    player.Powerups.Add(powerup);
    
    Assert.AreEqual(2, player.Damage);
  }
  
  [Test]
  public void TwoPowerupDamage()
  {
    var weapon = Substitute.For<Weapon>();
    weapon.Damage.Returns(1);
    var powerup = Substitute.For<IPowerup>();
    powerup.Multiplier.Returns(2);
    var player = new Player(weapon);
    
    player.Powerups.Add(powerup);
    player.Powerups.Add(powerup);
    
    Assert.AreEqual(4, player.Damage);
  }
  
  [Test]
  public void ThreePowerupDamage()
  {
    var weapon = Substitute.For<Weapon>();
    weapon.Damage.Returns(1);
    var powerup = Substitute.For<IPowerup>();
    powerup.Multiplier.Returns(2);
    var player = new Player(weapon);
    
    player.Powerups.Add(powerup);
    player.Powerups.Add(powerup);
    player.Powerups.Add(powerup);

    Assert.AreEqual(6, player.Damage);
  }
  
  [Test]
  public void FourPowerupDamage()
  {
    var weapon = Substitute.For<Weapon>();
    weapon.Damage.Returns(1);
    var powerup = Substitute.For<IPowerup>();
    powerup.Multiplier.Returns(2);
    var player = new Player(weapon);
    
    player.Powerups.Add(powerup);
    player.Powerups.Add(powerup);
    player.Powerups.Add(powerup);
    player.Powerups.Add(powerup);

    Assert.AreEqual(8, player.Damage);
  }
}