Why is Unit Testing So Hard - Example 3

why-is-unit-testing-so-hard-5.cs

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

public class Player : IPlayer
{
  private const int MaxPowerups = 3;

  private Weapon _weapon;

  public List<IPowerup> Powerups = { get; } = new List<IPowerup>();
  
  public double Damage => _weapon.Damage * Powerups.Take(MaxPowerups).Sum(p => p.Multiplier);
}

why-is-unit-testing-so-hard-6.cs

public class PlayerTest
{
  private IPowerup _powerup;
  private Weapon _weapon;

  [SetUp]
  public void Init()
  {
      _weapon = Substitute.For<Weapon>();
      _weapon.Damage.Returns(1);
      _powerup = Substitute.For<IPowerup>();
      _powerup.Multiplier.Returns(2);
  }

  [Test]
  public void PowerupDamage()
  {
      for (var i = 1; i < 4; i++)
      {
          var player = new Player(_weapon);

          for (var j = 0; j < i; j++)
          {
              player.Powerups.Add(_powerup);
          }
          Assert.AreEqual(CalculateDamage(_weapon, player.Powerups), player.Damage);
      }
  }

  public double CalculateDamage(Weapon weapon, List<IPowerup> powerups)
  {
      return weapon.Damage * powerups.Sum(p => p.Modifier);
  }
}