Update unit test

Author: SteveSandersonMS

src/Components/Server/test/Circuits/FixedAuthenticationStateProviderTest.cs

@@ -0,0 +1,49 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+using System.Security.Claims;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Components.Server.Circuits;
+using Xunit;
+
+namespace Microsoft.AspNetCore.Components.Server.Tests.Circuits
+{
+    public class ServerAuthenticationStateProviderTest
+    {
+        [Fact]
+        public async Task CannotProvideAuthenticationStateBeforeInitialization()
+        {
+            await Assert.ThrowsAsync<InvalidOperationException>(() =>
+                new ServerAuthenticationStateProvider()
+                    .GetAuthenticationStateAsync());
+        }
+
+        [Fact]
+        public async Task SuppliesAuthenticationStateWithFixedUser()
+        {
+            // Arrange
+            var user = new ClaimsPrincipal();
+            var provider = new ServerAuthenticationStateProvider();
+
+            // Act 1
+            var expectedAuthenticationState1 = new AuthenticationState(user);
+            provider.SetAuthenticationState(Task.FromResult(expectedAuthenticationState1));
+
+            // Assert 1
+            var actualAuthenticationState1 = await provider.GetAuthenticationStateAsync();
+            Assert.NotNull(actualAuthenticationState1);
+            Assert.Same(expectedAuthenticationState1, actualAuthenticationState1);
+
+            // Act 2: Show we can update it further
+            var expectedAuthenticationState2 = new AuthenticationState(user);
+            provider.SetAuthenticationState(Task.FromResult(expectedAuthenticationState2));
+
+            // Assert 2
+            var actualAuthenticationState2 = await provider.GetAuthenticationStateAsync();
+            Assert.NotNull(actualAuthenticationState2);
+            Assert.NotSame(actualAuthenticationState1, actualAuthenticationState2);
+            Assert.Same(expectedAuthenticationState2, actualAuthenticationState2);
+        }
+    }
+}