build(mps-legacy-sync-plugin): fix flaky test in `ReferenceSynchronis…

…ationTest`

The test did not account for that running `ISyncService.flushAllBindings` only flushed to the local modelix branch and did not guarantee to immediately sync to the model server.

Synchronization is scheduled by `org.modelix.model.client.ReplicatedRepository` on different thread.

Fixes: MODELIX-840

mps-legacy-sync-plugin/src/main/kotlin/org/modelix/mps/sync/api/ISyncService.kt

@@ -64,9 +64,12 @@ interface ISyncService {
     fun findMpsNode(cloudNodeReference: INodeReference): List<SNode>
 
     /**
-     * Synchronize all bindings between MPS and the model server.
+     * Synchronize all bindings between MPS and the local Modelix branch.
      * The call blocks until all synchronizations are finished or timeout.
      *
+     * It is not guaranteed that after invocation, the local Modelix branch has been synced to the model server.
+     * Synchronizing to the model server happens asynchronously in the background.
+     *
      * The synchronization is always scheduled on a different thread which will try to acquire a write and read lock.
      * To not deadlock your program, do not call this method while holding a write lock or read lock.
      */

mps-legacy-sync-plugin/src/test/kotlin/ReferenceSynchronisationTest.kt

@@ -90,7 +90,12 @@ class ReferenceSynchronisationTest : SyncPluginTestBase("projectWithReferences")
                     null,
                 )
             }
-            syncService.flushAllBindings()
+            delayUntil(exceptionMessage = "Failed to sync module to model server") {
+                val dataOnServer = readDumpFromServer(defaultBranchRef)
+                dataOnServer.children.any { module ->
+                    module.children.any { it.role == "models" }
+                }
+            }
 
             // Assert
             val rootNodeData = readDumpFromServer(defaultBranchRef)