test: add unit tests for ApiService.registerLocation

Cover success (200), duplicate (409), validation error (400), and
network failure paths using a MockClient.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

test/services/api_service_test.dart

@@ -0,0 +1,100 @@
+import 'dart:convert';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:http/http.dart' as http;
+import 'package:pad_scanner/services/api_service.dart';
+
+void main() {
+  group('ApiService.registerLocation', () {
+    test('returns ok on 200', () async {
+      final mockClient = _MockClient((request) async {
+        return http.Response(
+          jsonEncode({'zongpai_no': '26B1', 'location_code': 'A01-02-03', 'created_at': '2026-05-11T10:00:00'}),
+          200,
+          headers: {'content-type': 'application/json; charset=utf-8'},
+        );
+      });
+      final svc = ApiService(client: mockClient);
+      final result = await svc.registerLocation(
+        baseUrl: 'http://localhost',
+        zongpaiNo: '26B1',
+        locationCode: 'A01-02-03',
+      );
+      expect(result.success, isTrue);
+      expect(result.isDuplicate, isFalse);
+    });
+
+    test('returns duplicate on 409 with location_code and registered_at', () async {
+      final mockClient = _MockClient((request) async {
+        return http.Response(
+          jsonEncode({
+            'error_code': 'DUPLICATE_LOCATION',
+            'message': '该总排号已存在货位记录',
+            'location_code': 'A01-02-03',
+            'registered_at': '2026-05-11T10:00:00',
+          }),
+          409,
+          headers: {'content-type': 'application/json; charset=utf-8'},
+        );
+      });
+      final svc = ApiService(client: mockClient);
+      final result = await svc.registerLocation(
+        baseUrl: 'http://localhost',
+        zongpaiNo: '26B1',
+        locationCode: 'A02-01-01',
+      );
+      expect(result.success, isFalse);
+      expect(result.isDuplicate, isTrue);
+      expect(result.duplicateInfo?['location_code'], 'A01-02-03');
+      expect(result.duplicateInfo?['registered_at'], '2026-05-11T10:00:00');
+    });
+
+    test('returns error on 400 with message', () async {
+      final mockClient = _MockClient((request) async {
+        return http.Response(
+          jsonEncode({'error_code': 'INVALID_ZONGPAI', 'message': 'INVALID_ZONGPAI'}),
+          400,
+          headers: {'content-type': 'application/json; charset=utf-8'},
+        );
+      });
+      final svc = ApiService(client: mockClient);
+      final result = await svc.registerLocation(
+        baseUrl: 'http://localhost',
+        zongpaiNo: 'INVALID',
+        locationCode: 'A01-02-03',
+      );
+      expect(result.success, isFalse);
+      expect(result.isDuplicate, isFalse);
+      expect(result.errorMessage, 'INVALID_ZONGPAI');
+    });
+
+    test('returns error on network failure', () async {
+      final mockClient = _MockClient((request) async {
+        throw Exception('Connection refused');
+      });
+      final svc = ApiService(client: mockClient, timeout: Duration(seconds: 1));
+      final result = await svc.registerLocation(
+        baseUrl: 'http://localhost',
+        zongpaiNo: '26B1',
+        locationCode: 'A01-02-03',
+      );
+      expect(result.success, isFalse);
+      expect(result.errorMessage, '网络异常，请检查网络连接');
+    });
+  });
+}
+
+class _MockClient extends http.BaseClient {
+  final Future<http.Response> Function(http.BaseRequest) _handler;
+  _MockClient(this._handler);
+
+  @override
+  Future<http.StreamedResponse> send(http.BaseRequest request) async {
+    final response = await _handler(request);
+    return http.StreamedResponse(
+      http.ByteStream.fromBytes(response.bodyBytes),
+      response.statusCode,
+      headers: response.headers,
+      reasonPhrase: response.reasonPhrase,
+    );
+  }
+}