Revert "Merge pull request #9 from srawlins/remove-unused-imports"

This reverts commit 078f891d44c24942e1853519543287893092a425, reversing
changes made to 21c974622001431c1c2c61f9c827dd69b232f75b.

This commit seemed to cause the bots to go red under mysterious
circumstances. Reverting to determine why.
diff --git a/test/client/client_test.dart b/test/client/client_test.dart
index 5601daa..1553787 100644
--- a/test/client/client_test.dart
+++ b/test/client/client_test.dart
@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:async';
+import 'dart:convert';
 
 import 'package:test/test.dart';
 import 'package:json_rpc_2/error_code.dart' as error_code;
diff --git a/test/client/utils.dart b/test/client/utils.dart
index 09a200c..5eb0b60 100644
--- a/test/client/utils.dart
+++ b/test/client/utils.dart
@@ -9,6 +9,7 @@
 import 'package:test/test.dart';
 
 import 'package:json_rpc_2/json_rpc_2.dart' as json_rpc;
+import 'package:json_rpc_2/error_code.dart' as error_code;
 
 /// A controller used to test a [json_rpc.Client].
 class ClientController {
diff --git a/test/server/batch_test.dart b/test/server/batch_test.dart
index 11ec66e..d7bf79d 100644
--- a/test/server/batch_test.dart
+++ b/test/server/batch_test.dart
@@ -2,8 +2,11 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+import 'dart:convert';
+
 import 'package:test/test.dart';
 import 'package:json_rpc_2/error_code.dart' as error_code;
+import 'package:json_rpc_2/json_rpc_2.dart' as json_rpc;
 
 import 'utils.dart';
 
@@ -86,4 +89,4 @@
       }
     }])));
   });
-}
+}
\ No newline at end of file
diff --git a/test/server/invalid_request_test.dart b/test/server/invalid_request_test.dart
index cd54b6f..cd6f014 100644
--- a/test/server/invalid_request_test.dart
+++ b/test/server/invalid_request_test.dart
@@ -2,8 +2,11 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+import 'dart:convert';
+
 import 'package:test/test.dart';
 import 'package:json_rpc_2/error_code.dart' as error_code;
+import 'package:json_rpc_2/json_rpc_2.dart' as json_rpc;
 
 import 'utils.dart';