public void RemoveAll() { ICollection <int> collection = new HashSet <int> { 3, 4, 4, 5, 5, 5, 6, 6, 7, 8, 8, 8, 9 }; collection.Count.ShouldBe(7); collection.RemoveAll(i => i == 4).Count.ShouldBe(1); collection.Count.ShouldBe(6); collection.RemoveAll(i => i == 2).Count.ShouldBe(0); collection.Count.ShouldBe(6); collection.RemoveAll(i => i == 5).Count.ShouldBe(1); collection.Count.ShouldBe(5); }