Throw an exception when GraphSession already exists.

Author: peombwa

src/Authentication/Authentication.Test/Helpers/GraphSessionTests.cs

@@ -8,34 +8,44 @@ public class GraphSessionTests
         [Fact]
         public void GraphSessionShouldBeInitilizedAfterInitializerIsCalled()
         {
-            GraphSessionInitializer.InitializeSession();
+            GraphSession.Initialize(() => new GraphSession());
 
             Assert.NotNull(GraphSession.Instance);
             Assert.Null(GraphSession.Instance.AuthContext);
+
+            // reset static instance.
+            GraphSession.Reset();
         }
 
         [Fact]
         public void ShouldOverwriteExistingGraphSession()
         {
-            GraphSessionInitializer.InitializeSession();
+            GraphSession.Initialize(() => new GraphSession());
             Guid originalSessionId = GraphSession.Instance._graphSessionId;
 
             GraphSession.Initialize(() => new GraphSession(), true);
 
             Assert.NotNull(GraphSession.Instance);
-            Assert.NotEqual(GraphSession.Instance._graphSessionId, originalSessionId);
+            Assert.NotEqual(originalSessionId, GraphSession.Instance._graphSessionId);
+
+            // reset static instance.
+            GraphSession.Reset();
         } 
 
         [Fact]
         public void ShouldNotOverwriteExistingGraphSession()
         {
-            GraphSessionInitializer.InitializeSession();
+            GraphSession.Initialize(() => new GraphSession());
             Guid originalSessionId = GraphSession.Instance._graphSessionId;
 
-            GraphSession.Initialize(() => new GraphSession());
+            InvalidOperationException exception = Assert.Throws<InvalidOperationException>(() => GraphSession.Initialize(() => new GraphSession()));
 
+            Assert.Equal("An instance of GraphSession already exists. Call Initialize(Func<GraphSession>, bool) to overwrite it.", exception.Message);
             Assert.NotNull(GraphSession.Instance);
-            Assert.Equal(GraphSession.Instance._graphSessionId, originalSessionId);
+            Assert.Equal(originalSessionId, GraphSession.Instance._graphSessionId);
+
+            // reset static instance.
+            GraphSession.Reset();
         }
     }
 }

src/Authentication/Authentication.Test/Properties/AssemblyInfo.cs

@@ -0,0 +1,3 @@
+using Xunit;
+
+[assembly: CollectionBehavior(DisableTestParallelization = true)]

src/Authentication/Authentication/Common/GraphSession.cs

@@ -20,6 +20,10 @@ public class GraphSession : IGraphSession
         /// Gets or Sets <see cref="IAuthContext"/>.
         /// </summary>
         public IAuthContext AuthContext { get; set; }
+
+        /// <summary>
+        /// Gets an instance of <see cref="GraphSession"/>.
+        /// </summary>
         public static GraphSession Instance
         {
             get
@@ -50,6 +54,7 @@ public static GraphSession Instance
                 }
             }
         }
+
         /// <summary>
         /// Creates a new GraphSession.
         /// </summary>
@@ -75,6 +80,10 @@ public static void Initialize(Func<GraphSession> instanceCreator, bool overwrite
                         _instance = instanceCreator();
                         _initialized = true;
                     }
+                    else
+                    {
+                        throw new InvalidOperationException(string.Format(ErrorConstants.Message.InstanceExists, nameof(GraphSession), "Initialize(Func<GraphSession>, bool)"));
+                    }
                 }
                 finally
                 {
@@ -127,5 +136,33 @@ public static void Modify(Action<GraphSession> modifier)
                 throw new InvalidOperationException(ErrorConstants.Codes.SessionLockWriteDisposed, disposedException);
             }
         }
+
+        /// <summary>
+        /// Resets the current instance of <see cref="GraphSession"/> to initial state.
+        /// </summary>
+        internal static void Reset()
+        {
+            try
+            {
+                sessionLock.EnterWriteLock();
+                try
+                {
+                    _instance = null;
+                    _initialized = false;
+                }
+                finally
+                {
+                    sessionLock.ExitWriteLock();
+                }
+            }
+            catch (LockRecursionException lockException)
+            {
+                throw new InvalidOperationException(ErrorConstants.Codes.SessionLockWriteRecursion, lockException);
+            }
+            catch (ObjectDisposedException disposedException)
+            {
+                throw new InvalidOperationException(ErrorConstants.Codes.SessionLockWriteDisposed, disposedException);
+            }
+        }
     }
 }

src/Authentication/Authentication/ErrorConstants.cs

@@ -19,6 +19,7 @@ internal static class Message
         {
             internal const string InvalidJWT = "Invalid JWT access token.";
             internal const string MissingAuthContext = "Authentication needed, call Connect-Graph.";
+            internal const string InstanceExists = "An instance of {0} already exists. Call {1} to overwrite it.";
         }
     }
 }