public void TestUnionWith() { var a = new RedBlackSetTester<int>(_odd.Where(UpTo100)); Assert.That(() => a.SymmetricExceptWith(null), Throws.InstanceOf<ArgumentNullException>()); int count = a.Count; a.UnionWith(_primes); Assert.That(a.Count, Is.EqualTo(count + 1)); Assert.That(a.Contains(2)); a.UnionWith(_even.Where(UpTo100)); Assert.That(a.SetEquals(_numbers)); }