Fix non-idempotent Ghost API helper

- Add test
- Don't override apiUrl

closes #6239

core/shared/ghost-url.js

@@ -30,7 +30,8 @@
     url = {
         api: function () {
             var args = Array.prototype.slice.call(arguments),
-                queryOptions;
+                queryOptions,
+                requestUrl = apiUrl;
 
             if (args.length && typeof args[args.length - 1] === 'object') {
                 queryOptions = args.pop();
@@ -43,11 +44,11 @@
 
             if (args.length) {
                 args.forEach(function (el) {
-                    apiUrl += el.replace(/^\/|\/$/g, '') + '/';
+                    requestUrl += el.replace(/^\/|\/$/g, '') + '/';
                 });
             }
 
-            return apiUrl + generateQueryString(queryOptions);
+            return requestUrl + generateQueryString(queryOptions);
         }
     };
 

core/test/unit/ghost_url_spec.js

@@ -127,4 +127,20 @@ describe('Ghost Ajax Helper', function () {
         rendered.should.match(/include=tags%2Ctests/);
         rendered.should.match(/page=2/);
     });
+
+    it('should be idempotent', function () {
+        configUtils.set({
+            url: 'https://testblog.com/blog/'
+        });
+        ghostUrl.init({
+            clientId: 'ghost-frontend',
+            clientSecret: 'notasecret',
+            url: configUtils.config.apiUrl()
+        });
+
+        var rendered = ghostUrl.url.api('posts', {limit: 3}),
+            rendered2 = ghostUrl.url.api('posts', {limit: 3});
+
+        rendered.should.equal(rendered2);
+    });
 });