diff --git a/dio/test/options_test.dart b/dio/test/options_test.dart
index 960029430..64a9611af 100644
--- a/dio/test/options_test.dart
+++ b/dio/test/options_test.dart
@@ -13,39 +13,6 @@ import 'mock/http_mock.mocks.dart';
 import 'utils.dart';
 
 void main() {
-  setUp(startServer);
-  tearDown(stopServer);
-
-  test('headers are kept after redirects', () async {
-    final dio = Dio(
-      BaseOptions(
-        baseUrl: serverUrl.toString(),
-        headers: {'x-test-base': 'test-base'},
-      ),
-    );
-    final response = await dio.get(
-      '/redirect',
-      options: Options(headers: {'x-test-header': 'test-value'}),
-    );
-    expect(response.isRedirect, isTrue);
-    expect(
-      response.data['headers']['x-test-base'].single,
-      equals('test-base'),
-    );
-    expect(
-      response.data['headers']['x-test-header'].single,
-      equals('test-value'),
-    );
-    expect(
-      response.requestOptions.headers['x-test-base'],
-      equals('test-base'),
-    );
-    expect(
-      response.requestOptions.headers['x-test-header'],
-      equals('test-value'),
-    );
-  });
-
   test('options', () {
     final map = {'a': '5'};
     final mapOverride = {'b': '6'};
@@ -256,113 +223,6 @@ void main() {
     ro3.copyWith();
   });
 
-  test('default content-type', () async {
-    final dio = Dio();
-    dio.options.baseUrl = EchoAdapter.mockBase;
-    dio.httpClientAdapter = EchoAdapter();
-
-    final r1 = await dio.get('');
-    expect(
-      r1.requestOptions.headers[Headers.contentTypeHeader],
-      null,
-    );
-
-    final r2 = await dio.get(
-      '',
-      options: Options(contentType: Headers.jsonContentType),
-    );
-    expect(
-      r2.requestOptions.headers[Headers.contentTypeHeader],
-      Headers.jsonContentType,
-    );
-
-    final r3 = await dio.get(
-      '',
-      options: Options(
-        headers: {Headers.contentTypeHeader: Headers.jsonContentType},
-      ),
-    );
-    expect(
-      r3.requestOptions.headers[Headers.contentTypeHeader],
-      Headers.jsonContentType,
-    );
-
-    final r4 = await dio.post('', data: '');
-    expect(
-      r4.requestOptions.headers[Headers.contentTypeHeader],
-      Headers.jsonContentType,
-    );
-
-    final r5 = await dio.get(
-      '',
-      options: Options(
-        // Final result should respect this.
-        contentType: Headers.textPlainContentType,
-        // Rather than this.
-        headers: {Headers.contentTypeHeader: Headers.formUrlEncodedContentType},
-      ),
-    );
-    expect(
-      r5.requestOptions.headers[Headers.contentTypeHeader],
-      Headers.textPlainContentType,
-    );
-
-    final r6 = await dio.get(
-      '',
-      data: '',
-      options: Options(
-        contentType: Headers.formUrlEncodedContentType,
-        headers: {Headers.contentTypeHeader: Headers.jsonContentType},
-      ),
-    );
-    expect(
-      r6.requestOptions.headers[Headers.contentTypeHeader],
-      Headers.formUrlEncodedContentType,
-    );
-
-    // Update the base option.
-    dio.options.contentType = Headers.textPlainContentType;
-    final r7 = await dio.get('');
-    expect(
-      r7.requestOptions.headers[Headers.contentTypeHeader],
-      Headers.textPlainContentType,
-    );
-
-    final r8 = await dio.get(
-      '',
-      options: Options(contentType: Headers.jsonContentType),
-    );
-    expect(
-      r8.requestOptions.headers[Headers.contentTypeHeader],
-      Headers.jsonContentType,
-    );
-
-    final r9 = await dio.get(
-      '',
-      options: Options(
-        headers: {Headers.contentTypeHeader: Headers.jsonContentType},
-      ),
-    );
-    expect(
-      r9.requestOptions.headers[Headers.contentTypeHeader],
-      Headers.jsonContentType,
-    );
-
-    final r10 = await dio.post('', data: FormData());
-    expect(
-      r10.requestOptions.contentType,
-      startsWith(Headers.multipartFormDataContentType),
-    );
-
-    // Regression: https://github.com/cfug/dio/issues/1834
-    final r11 = await dio.get('');
-    expect(r11.data, '');
-    final r12 = await dio.get<Map>('');
-    expect(r12.data, null);
-    final r13 = await dio.get<Map<String, Object>>('');
-    expect(r13.data, null);
-  });
-
   test('default content-type 2', () async {
     final dio = Dio();
     dio.options.baseUrl = 'https://www.example.com';
diff --git a/dio_test/lib/src/test/headers_tests.dart b/dio_test/lib/src/test/headers_tests.dart
index 46298b742..29ea34339 100644
--- a/dio_test/lib/src/test/headers_tests.dart
+++ b/dio_test/lib/src/test/headers_tests.dart
@@ -49,5 +49,142 @@ void headerTests(
       expect(content, contains('Numkey: 2'));
       expect(content, contains('Booleankey: false'));
     });
+
+    test(
+      'headers are kept after redirects',
+      () async {
+        dio.options.headers.putIfAbsent('x-test-base', () => 'test-base');
+
+        final response = await dio.get(
+          '/redirect/3',
+          options: Options(headers: {'x-test-header': 'test-value'}),
+        );
+        expect(response.isRedirect, isTrue);
+        // The returned headers are uppercased by the server.
+        expect(
+          response.data['headers']['X-Test-Base'],
+          equals('test-base'),
+        );
+        expect(
+          response.data['headers']['X-Test-Header'],
+          equals('test-value'),
+        );
+        // The sent headers are still lowercase.
+        expect(
+          response.requestOptions.headers['x-test-base'],
+          equals('test-base'),
+        );
+        expect(
+          response.requestOptions.headers['x-test-header'],
+          equals('test-value'),
+        );
+      },
+      testOn: 'vm',
+    );
+
+    test('default content-type', () async {
+      final r1 = await dio.get('/get');
+      expect(
+        r1.requestOptions.headers[Headers.contentTypeHeader],
+        null,
+      );
+
+      final r2 = await dio.get(
+        '/get',
+        options: Options(contentType: Headers.jsonContentType),
+      );
+      expect(
+        r2.requestOptions.headers[Headers.contentTypeHeader],
+        Headers.jsonContentType,
+      );
+
+      final r3 = await dio.get(
+        '/get',
+        options: Options(
+          headers: {Headers.contentTypeHeader: Headers.jsonContentType},
+        ),
+      );
+      expect(
+        r3.requestOptions.headers[Headers.contentTypeHeader],
+        Headers.jsonContentType,
+      );
+
+      final r4 = await dio.post('/post', data: '');
+      expect(
+        r4.requestOptions.headers[Headers.contentTypeHeader],
+        Headers.jsonContentType,
+      );
+
+      final r5 = await dio.get(
+        '/get',
+        options: Options(
+          // Final result should respect this.
+          contentType: Headers.textPlainContentType,
+          // Rather than this.
+          headers: {
+            Headers.contentTypeHeader: Headers.formUrlEncodedContentType
+          },
+        ),
+      );
+      expect(
+        r5.requestOptions.headers[Headers.contentTypeHeader],
+        Headers.textPlainContentType,
+      );
+
+      final r6 = await dio.get(
+        '/get',
+        data: '',
+        options: Options(
+          contentType: Headers.formUrlEncodedContentType,
+          headers: {Headers.contentTypeHeader: Headers.jsonContentType},
+        ),
+      );
+      expect(
+        r6.requestOptions.headers[Headers.contentTypeHeader],
+        Headers.formUrlEncodedContentType,
+      );
+
+      // Update the base option.
+      dio.options.contentType = Headers.textPlainContentType;
+      final r7 = await dio.get('/get');
+      expect(
+        r7.requestOptions.headers[Headers.contentTypeHeader],
+        Headers.textPlainContentType,
+      );
+
+      final r8 = await dio.get(
+        '/get',
+        options: Options(contentType: Headers.jsonContentType),
+      );
+      expect(
+        r8.requestOptions.headers[Headers.contentTypeHeader],
+        Headers.jsonContentType,
+      );
+
+      final r9 = await dio.get(
+        '/get',
+        options: Options(
+          headers: {Headers.contentTypeHeader: Headers.jsonContentType},
+        ),
+      );
+      expect(
+        r9.requestOptions.headers[Headers.contentTypeHeader],
+        Headers.jsonContentType,
+      );
+
+      final r10 = await dio.post('/post', data: FormData());
+      expect(
+        r10.requestOptions.contentType,
+        startsWith(Headers.multipartFormDataContentType),
+      );
+
+      // Regression: https://github.com/cfug/dio/issues/1834
+      final r11 = await dio.get('/payload');
+      expect(r11.data, '');
+      final r12 = await dio.get<Map>('/payload');
+      expect(r12.data, null);
+      final r13 = await dio.get<Map<String, Object>>('/payload');
+      expect(r13.data, null);
+    });
   });
 }