Empty code coverage.

Ix.NET/Source/System.Linq.Async.Tests/System/Linq/Operators/Empty.cs

@@ -2,6 +2,7 @@
 // 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;
@@ -11,10 +12,30 @@ namespace Tests
     public class Empty : AsyncEnumerableTests
     {
         [Fact]
-        public async Task Empty1()
+        public async Task Empty_Basics()
         {
             var xs = AsyncEnumerable.Empty<int>();
+
             await NoNextAsync(xs.GetAsyncEnumerator());
+
+            Assert.Equal(0, xs.GetAsyncEnumerator().Current);
+        }
+
+        [Fact]
+        public async Task Empty_IAsyncPartition()
+        {
+            var xs = AsyncEnumerable.Empty<int>();
+
+            Assert.Equal(0, await xs.CountAsync());
+            Assert.Equal(0, await xs.Skip(1).CountAsync());
+            Assert.Equal(0, await xs.Take(1).CountAsync());
+
+            await AssertThrowsAsync<InvalidOperationException>(xs.FirstAsync().AsTask());
+            await AssertThrowsAsync<InvalidOperationException>(xs.LastAsync().AsTask());
+            await AssertThrowsAsync<InvalidOperationException>(xs.SingleAsync().AsTask());
+
+            Assert.Empty(await xs.ToArrayAsync());
+            Assert.Empty(await xs.ToListAsync());
         }
     }
 }