Add test for get followers (#765)

I found
[`pytest_httpserve`](https://pytest-httpserver.readthedocs.io/en/latest/)
to be more convenient compared to other mock servers.
This change just adds missing unit tests.

Author: Yang-33

requirements-test.txt

@@ -3,3 +3,4 @@ pytest-pep8
 pytest-cov
 pytest-aiohttp
 responses
+pytest_httpserver >= 1.1.2

tests/v3/messaging/test_get_followers.py

@@ -0,0 +1,106 @@
+# -*- coding: utf-8 -*-
+
+#  Licensed under the Apache License, Version 2.0 (the "License"); you may
+#  not use this file except in compliance with the License. You may obtain
+#  a copy of the License at
+#
+#       https://www.apache.org/licenses/LICENSE-2.0
+#
+#  Unless required by applicable law or agreed to in writing, software
+#  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#  License for the specific language governing permissions and limitations
+#  under the License.
+
+import unittest
+from pytest_httpserver.httpserver import HTTPServer
+
+from linebot.v3.messaging import (
+    Configuration,
+    ApiClient,
+    MessagingApi,
+)
+
+
+class TestGetFollowersWithQueryParam(unittest.TestCase):
+    def test_get_followers_with_query(self):
+        expected_response = {
+            "userIds": [
+                "U4af4980629",
+                "U0c229f96c4",
+                "U95afb1d4df"
+            ],
+            "next": "yANU9IA..."
+        }
+
+        with HTTPServer() as httpserver:
+            httpserver.expect_request(
+                uri="/v2/bot/followers/ids",
+                method="GET",
+            ).respond_with_json(
+                expected_response,
+                status=200
+            )
+
+            configuration = Configuration(
+                access_token="dummy-channel-access-token",
+                host=httpserver.url_for("/")
+            )
+
+            with ApiClient(configuration) as api_client:
+                line_bot_api = MessagingApi(api_client)
+                response = line_bot_api.get_followers()
+
+            # Verify response
+            self.assertEqual(response.user_ids, expected_response["userIds"])
+            self.assertEqual(response.next, expected_response["next"])
+
+            # Verify request details
+            self.assertEqual(len(httpserver.log), 1)
+            req, res = httpserver.log[0]
+            self.assertEqual(req.method, "GET")
+            self.assertEqual(req.path, "/v2/bot/followers/ids")
+            self.assertEqual(req.query_string, b"")
+
+    def test_get_followers_with_start(self):
+        expected_response = {
+            "userIds": [
+                "U4af4980629",
+                "U0c229f96c4",
+                "U95afb1d4df"
+            ],
+            "next": "yANU9IA..."
+        }
+
+        with HTTPServer() as httpserver:
+            httpserver.expect_request(
+                uri="/v2/bot/followers/ids",
+                method="GET",
+            ).respond_with_json(
+                expected_response,
+                status=200
+            )
+
+            configuration = Configuration(
+                access_token="dummy-channel-access-token",
+                host=httpserver.url_for("/")
+            )
+
+            with ApiClient(configuration) as api_client:
+                line_bot_api = MessagingApi(api_client)
+                response = line_bot_api.get_followers(start="dummy-start", limit=123)
+
+            # Verify response
+            self.assertEqual(response.user_ids, expected_response["userIds"])
+            self.assertEqual(response.next, expected_response["next"])
+
+            # Verify request details
+            self.assertEqual(len(httpserver.log), 1)
+            req, res = httpserver.log[0]
+            self.assertEqual(req.method, "GET")
+            self.assertEqual(req.path, "/v2/bot/followers/ids")
+            self.assertEqual(req.query_string, b"start=dummy-start&limit=123")
+
+
+if __name__ == '__main__':
+    unittest.main()