diff --git a/umap/static/umap/js/modules/sync/engine.js b/umap/static/umap/js/modules/sync/engine.js
index 5009d53f..9c4f15e6 100644
--- a/umap/static/umap/js/modules/sync/engine.js
+++ b/umap/static/umap/js/modules/sync/engine.js
@@ -47,10 +47,11 @@ export class MessagesDispatcher {
   }
 
   dispatch({ kind, ...payload }) {
-    console.log('received message', kind, payload)
     if (kind == 'operation') {
       let updater = this.getUpdater(payload.subject, payload.metadata)
       updater.applyMessage(payload)
+    } else {
+      throw new Error(`Unknown dispatch kind: ${kind}`)
     }
   }
 }
diff --git a/umap/static/umap/js/modules/sync/updaters.js b/umap/static/umap/js/modules/sync/updaters.js
index e934434b..d7a45492 100644
--- a/umap/static/umap/js/modules/sync/updaters.js
+++ b/umap/static/umap/js/modules/sync/updaters.js
@@ -20,7 +20,7 @@ class BaseUpdater {
       if (part in currentObj) return currentObj[part]
     }, obj)
 
-    // In case the given path doesn't exist, bail out
+    // In case the given path doesn't exist, stop here
     if (objectToSet === undefined) return
 
     // Set the value (or delete it)
diff --git a/umap/static/umap/unittests/updaters.js b/umap/static/umap/unittests/sync.js
similarity index 61%
rename from umap/static/umap/unittests/updaters.js
rename to umap/static/umap/unittests/sync.js
index 7a60a544..a7eb464b 100644
--- a/umap/static/umap/unittests/updaters.js
+++ b/umap/static/umap/unittests/sync.js
@@ -1,13 +1,52 @@
 import { describe, it } from 'mocha'
+import sinon from 'sinon'
 
 import pkg from 'chai'
 const { expect } = pkg
 
-import {
-  MapUpdater,
-  DataLayerUpdater,
-  FeatureUpdater,
-} from '../js/modules/sync/updaters.js'
+import { MapUpdater } from '../js/modules/sync/updaters.js'
+import { MessagesDispatcher, SyncEngine } from '../js/modules/sync/engine.js'
+
+describe('SyncEngine', () => {
+  it('should initialize methods even before start', function () {
+    const engine = new SyncEngine({})
+    engine.upsert()
+    engine.update()
+    engine.delete()
+  })
+})
+
+describe('MessageDispatcher', () => {
+  describe('#dispatch', function () {
+    it('should raise an error on unknown updater', function () {
+      const dispatcher = new MessagesDispatcher({})
+      expect(() => {
+        dispatcher.dispatch({
+          kind: 'operation',
+          subject: 'unknown',
+          metadata: {},
+        })
+      }).to.throw(Error)
+    })
+    it('should produce an error on malformated messages', function () {
+      const dispatcher = new MessagesDispatcher({})
+      expect(() => {
+        dispatcher.dispatch({
+          yeah: 'yeah',
+          payload: { foo: 'bar' },
+        })
+      }).to.throw(Error)
+    })
+    it('should raise an unknown operations', function () {
+      const dispatcher = new MessagesDispatcher({})
+      expect(() => {
+        dispatcher.dispatch({
+          kind: 'something-else',
+        })
+      }).to.throw(Error)
+    })
+  })
+})
 
 describe('Updaters', () => {
   describe('BaseUpdater', function () {