Add StompConfig test

test/stomp_config_test.dart

@@ -0,0 +1,47 @@
+import 'dart:async';
+
+import 'package:test/test.dart';
+import 'package:web_socket_channel/web_socket_channel.dart';
+
+import 'package:stomp_dart_client/stomp_config.dart';
+import 'package:stomp_dart_client/src/_connect_api.dart'
+    if (dart.library.html) '../lib/src/_connect_html.dart'
+    if (dart.library.io) '../lib/src/_connect_io.dart' as platform;
+
+void main() {
+  group('StompConfig', () {
+    test('Generate session URL once per connection', () async {
+      final config = StompConfig.sockJS(
+        url: 'http://localhost',
+        reconnectDelay: Duration(milliseconds: 500),
+      );
+
+      final connectUrls = <(String, String)>[];
+
+      void connect() async {
+        try {
+          await platform.connect(config..resetSession());
+        } on WebSocketChannelException catch (_) {
+          // Save subsequent calls of `connectUrl`.
+          connectUrls.add((config.connectUrl, config.connectUrl));
+          if (connectUrls.length == 1) {
+            // On 1st connect we expect that the current stored values are equal
+            expect(connectUrls.first.$1, equals(connectUrls.first.$2));
+          } else if (connectUrls.length == 2) {
+            // On 2nd connect we expect that the current stored values are equal
+            expect(connectUrls.last.$1, equals(connectUrls.last.$2));
+            // But they are different from the values saved on 1st connect
+            expect(connectUrls.first.$1, isNot(equals(connectUrls.last.$1)));
+            expect(connectUrls.first.$2, isNot(equals(connectUrls.last.$2)));
+          }
+          Timer(config.reconnectDelay, connect);
+        }
+      }
+
+      connect();
+
+      // Wait until exit
+      await Future.delayed(Duration(seconds: 3));
+    });
+  });
+}