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));
}
