chore: Add extra condition for emulator tests with concurrent txn

Author: purvavasudeo

apis/Google.Cloud.Spanner.Data/Google.Cloud.Spanner.Data/SessionPoolManager.cs

@@ -163,11 +163,22 @@ internal Task<ManagedSession> AcquireManagedSessionAsync(SpannerClientCreationOp
         {
             SessionPoolSegmentKey segmentKey = SessionPoolSegmentKey.Create(dbName).WithDatabaseRole(dbRole);
             GaxPreconditions.CheckNotNull(options, nameof(options));
+            Lazy<Task<ManagedSession>> lazyManagedSessionTask;
 
-            // To work around nuances of how value factory execution works in a concurrent dictionary
-            // We need to wrap the call to CreateMultiplexSessionAsync() in a LazyTask
-            // to avoid concurrent threads spinning off multiple executions of CreateMultiplexSessionAsync()
-            var lazyManagedSessionTask = _targetedSessions.GetOrAdd((options, segmentKey), _ => new Lazy<Task<ManagedSession>>(CreateMultiplexSessionAsync, LazyThreadSafetyMode.ExecutionAndPublication));
+            if (!string.IsNullOrEmpty(Environment.GetEnvironmentVariable("SPANNER_EMULATOR_HOST")) && _targetedSessions.ContainsKey((options, segmentKey)))
+            {
+                // The Spanner Emulator has a limitation that it does not support concurrent transactions on a single multiplex session.
+                // To make sure async integration tests (which basically mimic concurrent transactions) work, we need to create a new session instance each time
+                lazyManagedSessionTask = _targetedSessions[(options, segmentKey)] = new Lazy<Task<ManagedSession>>(CreateMultiplexSessionAsync, LazyThreadSafetyMode.ExecutionAndPublication);
+            }
+            else
+            {
+                // To work around nuances of how value factory execution works in a concurrent dictionary
+                // We need to wrap the call to CreateMultiplexSessionAsync() in a LazyTask
+                // to avoid concurrent threads spinning off multiple executions of CreateMultiplexSessionAsync()
+                lazyManagedSessionTask = _targetedSessions.GetOrAdd((options, segmentKey), _ => new Lazy<Task<ManagedSession>>(CreateMultiplexSessionAsync, LazyThreadSafetyMode.ExecutionAndPublication));
+
+            }
 
             return lazyManagedSessionTask.Value;