feat(auth): 登录页改为 ymb 品牌并支持后台配置背景图

test/core/app_config_controller_test.dart

@@ -0,0 +1,53 @@
+// Author: fruit.com.cn
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:fruitshorts/core/data/remote/api_client.dart';
+import 'package:fruitshorts/core/data/remote/config_api.dart';
+import 'package:fruitshorts/core/data/services/app_config_controller.dart';
+
+import '../support/fake_http_adapter.dart';
+
+AppConfigController _controller(FakeHttpAdapter adapter) => AppConfigController(
+  ConfigApi(ApiClient(baseUrl: 'http://127.0.0.1:1', adapter: adapter)),
+);
+
+void main() {
+  test('should_use_backend_url_when_login_background_is_configured', () async {
+    final controller = _controller(
+      FakeHttpAdapter(
+        (_) async => FakeHttpResponse(
+          '{"code":0,"data":{"loginBackgroundUrl":"/files/login_bg/bg.jpg"}}',
+        ),
+      ),
+    );
+
+    await controller.load();
+
+    expect(controller.loginBackgroundUrl, '/files/login_bg/bg.jpg');
+  });
+
+  test('should_treat_blank_value_as_not_configured', () async {
+    final controller = _controller(
+      FakeHttpAdapter(
+        (_) async =>
+            FakeHttpResponse('{"code":0,"data":{"loginBackgroundUrl":"  "}}'),
+      ),
+    );
+
+    await controller.load();
+
+    expect(controller.loginBackgroundUrl, isEmpty);
+  });
+
+  test('should_keep_local_default_when_config_request_fails', () async {
+    var notified = 0;
+    final controller = _controller(
+      FakeHttpAdapter((_) async => FakeHttpResponse('{}', 500)),
+    )..addListener(() => notified++);
+
+    await controller.load();
+
+    expect(controller.loginBackgroundUrl, isEmpty);
+    expect(notified, 0);
+  });
+}