Pooled integration instances now get marked non-idle

Otherwise, pooled integration instances could behave differently from freshly-spawned ones, creating heisentests.

RELEASE-NOTES.md

@@ -43,7 +43,7 @@ END TEMPLATE-->
 
 ### Bugfixes
 
-*None yet*
+* Pooled integration instances returned by `RobustIntegrationTest` are now treated as non-idle, for consistency with non-pooled startups.
 
 ### Other
 

Robust.UnitTesting/RobustIntegrationTest.cs

@@ -94,6 +94,10 @@ namespace Robust.UnitTesting
 
                     OnServerReturn(server).Wait();
 
+                    // Ensure the instance is properly idle to avoid inconsistencies in behavior
+                    // between pooled and non-pooled returns.
+                    server.MarkNonIdle();
+
                     _serversRunning[server] = 0;
                     instance = server;
                 }
@@ -139,6 +143,10 @@ namespace Robust.UnitTesting
 
                     OnClientReturn(client).Wait();
 
+                    // Ensure the instance is properly idle to avoid inconsistencies in behavior
+                    // between pooled and non-pooled returns.
+                    client.MarkNonIdle();
+
                     _clientsRunning[client] = 0;
                     instance = client;
                 }
@@ -602,6 +610,11 @@ namespace Robust.UnitTesting
                 await WaitIdleAsync();
             }
 
+            internal void MarkNonIdle()
+            {
+                Post(() => {});
+            }
+
             public virtual Task Cleanup() => Task.CompletedTask;
 
             public void Dispose()