Add missing sync error (#925)

* Add missing sync error

* Make unit tests work without sync

* Wording fix

lib/extensions.js

@@ -66,6 +66,12 @@ module.exports = function(realmConstructor) {
 
         setConstructorOnPrototype(realmConstructor.Sync.User);
         setConstructorOnPrototype(realmConstructor.Sync.Session);
+    } else {
+        Object.defineProperty(realmConstructor, 'Sync', {
+            get: function () {
+                throw new Error("Realm.Sync is not available. Note that the developer edition of the Node.JS SDK for Realm does not include sync on Linux.");
+            }
+        })
     }
 
     // TODO: Remove this now useless object.
@@ -99,4 +105,4 @@ module.exports = function(realmConstructor) {
         },
         configurable: true
     });
-}
+}

tests/js/index.js

@@ -35,10 +35,11 @@ if (!(typeof process === 'object' && process.platform === 'win32')) {
 }
 
 // If sync is enabled, run the user tests
-if (Realm.Sync) {
+try {
+    Realm.Sync; // This will throw if Sync is disabled.
     TESTS.UserTests = require('./user-tests');
     TESTS.SessionTests = require('./session-tests');
-}
+} catch (e) {}
 
 function node_require(module) { return require(module); }