System.Linq.Tests.SelectTests.Select_SourceIsIList_First C# (CSharp) Метод

        public void Select_SourceIsIList_First()
        {
            var source = new List<int> { 1, 2, 3, 4 }.AsReadOnly().Select(i => i * 2);
            Assert.Equal(2, source.First());
            Assert.Equal(2, source.FirstOrDefault());

            Assert.Equal(6, source.Skip(2).First());
            Assert.Equal(6, source.Skip(2).FirstOrDefault());
            Assert.Throws<InvalidOperationException>(() => source.Skip(4).First());
            Assert.Throws<InvalidOperationException>(() => source.Skip(14).First());
            Assert.Equal(0, source.Skip(4).FirstOrDefault());
            Assert.Equal(0, source.Skip(14).FirstOrDefault());

            var empty = new List<int>().AsReadOnly().Select(i => i * 2);
            Assert.Throws<InvalidOperationException>(() => empty.First());
            Assert.Equal(0, empty.FirstOrDefault());
        }