[MM-34836] Cleanse URLs of extra slashes on parsing, and add the image proxy case (#1560)

* [MM-34836] Cleanse URLs of extra slashes on parsing, and add the image proxy case

* Added unit tests

test/unit/index.js

@@ -2,3 +2,4 @@
 // See LICENSE.txt for license information.
 
 import './trusted_origins_test';
+import './url_test';

test/unit/url_test.js

@@ -0,0 +1,18 @@
+// Copyright (c) 2016-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+'use strict';
+
+import assert from 'assert';
+
+import urlUtils from 'common/utils/url';
+
+describe('URL', () => {
+    describe('parseURL', () => {
+        it('should remove duplicate slashes in a URL when parsing', () => {
+            const urlWithExtraSlashes = 'https://mattermost.com//sub//path//example';
+            const parsedURL = urlUtils.parseURL(urlWithExtraSlashes);
+
+            assert.strictEqual(parsedURL.toString(), 'https://mattermost.com/sub/path/example');
+        });
+    });
+});