public void TestHashSetEqualityComparer()
{
var data = new[] { "foo", "bar", "foobar" };
var set1 = new HashSet <string>(data, StringComparer.Ordinal);
var set2 = new HashSet <string>(data, StringComparer.OrdinalIgnoreCase);
var comparer = HashSetEx <string> .CreateSetComparer();
Assert.IsTrue(comparer.Equals(set1, set1));
Assert.IsTrue(comparer.Equals(set1, set2));
Assert.AreEqual(comparer.GetHashCode(set1), comparer.GetHashCode(set2));
var set3 = new HashSet <string>(new[] { "foobar", "foo", "bar" });
Assert.IsTrue(comparer.Equals(set1, set3));
Assert.AreEqual(comparer.GetHashCode(set1), comparer.GetHashCode(set3));
var set4 = new HashSet <string>(new[] { "oh", "hai", "folks" });
Assert.IsFalse(comparer.Equals(set2, set4));
Assert.AreNotEqual(comparer.GetHashCode(set2), comparer.GetHashCode(set4));
Assert.IsTrue(comparer.Equals(null, null));
// ReSharper disable once AssignNullToNotNullAttribute
Assert.AreEqual(0, comparer.GetHashCode(null));
Assert.IsFalse(comparer.Equals(set1, null));
}