System.Tests.StringTests.GetEnumerator_NonGeneric_Invalid C# (CSharp) Method

        public static void GetEnumerator_NonGeneric_Invalid()
        {
            IEnumerable enumerable = "foo";
            IEnumerator enumerator = enumerable.GetEnumerator();

            // Enumerator should throw when accessing Current before starting enumeration
            Assert.Throws<InvalidOperationException>(() => enumerator.Current);
            while (enumerator.MoveNext()) ;

            // Enumerator should throw when accessing Current after finishing enumeration
            Assert.False(enumerator.MoveNext());
            Assert.Throws<InvalidOperationException>(() => enumerator.Current);

            // Enumerator should throw when accessing Current after being reset
            enumerator.Reset();
            Assert.Throws<InvalidOperationException>(() => enumerator.Current);
        }