public void AddAndRemoveComponent()
{
Assert.AreEqual(1, entities.NumberOfEntities);
var entity = new MockEntity().Add(new object());
Assert.AreEqual(2, entities.NumberOfEntities);
Assert.AreEqual(1, entity.NumberOfComponents);
Assert.IsNotNull(entity.Get<object>());
entity.Remove<object>();
Assert.AreEqual(0, entity.NumberOfComponents);
Assert.IsFalse(entity.Contains<object>());
Assert.Throws<ArgumentNullException>(() => new MockEntity().Add<object>(null));
}