reactive/Ix.NET/Source/System.Linq.Async.Tests/System/Linq/Operators/Cast.cs

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the Apache 2.0 License.
// See the LICENSE file in the project root for more information. 

using System;
using System.Linq;
using System.Threading.Tasks;
using Xunit;

namespace Tests
{
    public class Cast : AsyncEnumerableTests
    {
        [Fact]
        public void Cast_Null()
        {
            Assert.Throws<ArgumentNullException>(() => AsyncEnumerable.Cast<int>(default));
        }

        [Fact]
        public async Task Cast_References()
        {
            var xs = new object[] { "bar", "foo", "qux" }.ToAsyncEnumerable();
            var ys = xs.Cast<string>();

            var e = ys.GetAsyncEnumerator();
            await HasNextAsync(e, "bar");
            await HasNextAsync(e, "foo");
            await HasNextAsync(e, "qux");
            await NoNextAsync(e);
        }

        [Fact]
        public async Task Cast_Values()
        {
            var xs = new object[] { 1, 2, 3, 4 }.ToAsyncEnumerable();
            var ys = xs.Cast<int>();

            var e = ys.GetAsyncEnumerator();
            await HasNextAsync(e, 1);
            await HasNextAsync(e, 2);
            await HasNextAsync(e, 3);
            await HasNextAsync(e, 4);
            await NoNextAsync(e);
        }

        [Fact]
        public async Task Cast_InvalidCast()
        {
            var xs = new object[] { 42, "foo", 43 }.ToAsyncEnumerable();
            var ys = xs.Cast<int>();

            var e = ys.GetAsyncEnumerator();
            await HasNextAsync(e, 42);
            await AssertThrowsAsync<InvalidCastException>(e.MoveNextAsync().AsTask());
        }

        [Fact]
        public void Cast_Aliasing()
        {
            var xs = new[] { new EventArgs(), new EventArgs(), new EventArgs() }.ToAsyncEnumerable();
            var ys = xs.Cast<EventArgs>();

            Assert.Same(xs, ys);
        }
    }
}