public void OnePropertyValueShouldBeAppended(PropertyValueCollection collection)
{
// Fixture setup
collection.SetValue(DirectoryProperty.Member, DN.Parse(john));
// Exercise system
collection.AppendValue(DirectoryProperty.Member, DN.Parse(paul));
// Verify outcome
collection.GetValues <DN>(DirectoryProperty.Member)
.Should().BeEquivalentTo(DN.Parse(john), DN.Parse(paul));
}