public void random_enumerable() { Assert.Throws<ArgumentNullException>(() => ((IEnumerable<IEntity>)null).Random()); Assert.Null(Enumerable.Empty<IEntity>().Random()); var first = new Entity { Id = 1 }; var second = new Entity { Id = 2 }; var entities = new IEntity[] { first, second }; Assert.Same(first, new IEntity[] { first }.Random()); Assert.Contains(entities.Random(), entities); }