Tweak read preference tag groups url conversion, add tests (#289)

Author: Anemy

lib/model.js

@@ -552,11 +552,15 @@ const prepareRequest = (model) => {
         }
       } else if (item === 'readPreferenceTags') {
         if (model.readPreferenceTags) {
-          req.query.readPreferenceTags = Object.keys(
+          req.query.readPreferenceTags = Object.values(
             model.readPreferenceTags
-          )
-            .map(tag => `${tag}:${model.readPreferenceTags[tag]}`)
-            .join(',');
+          ).map(
+            tagGroup => Object.keys(
+              tagGroup
+            )
+              .map(tag => `${tag}:${tagGroup[tag]}`)
+              .join(',')
+          );
         }
       } else if (model[item] !== '') {
         req.query[item] = model[item];

test/parse-and-build-uri.js

@@ -72,7 +72,14 @@ const tests = [
       'with readPreference, maxStalenessSeconds and readPreferenceTags',
     connectionString:
       'mongodb://mongos1.example.com:27017,mongos2.example.com:27017/?' +
-      'readPreference=secondary&maxStalenessSeconds=120&readPreferenceTags=0%3A%5Bobject%20Object%5D&ssl=false'
+      'readPreference=secondary&maxStalenessSeconds=120&readPreferenceTags=dc%3Any%2Crack%3A1&ssl=false'
+  },
+  {
+    description:
+      'with multiple readPreferenceTags',
+    connectionString:
+      'mongodb://mongos1.example.com:27017,mongos2.example.com:27017/?' +
+      'readPreference=primary&readPreferenceTags=dc%3Any%2Crack%3A1&readPreferenceTags=region%3Anorth%2Cdatacenter%3AA&ssl=false'
   },
   {
     description: 'with authSource and authMechanism',