Enable linting of test folder

When we initially set up the lint make target, we forgot to include
the tests folder in the flake8 check. This commit makes sure tests are
also linted and fixes the issue we managed to accrue in our unit
tests.

Author: Tadej Borovšak

Makefile

@@ -11,7 +11,7 @@ format:
 .PHONY: lint
 lint:
 	venv/bin/black --check --diff src/sensu_go tests
-	venv/bin/flake8 src/sensu_go
+	venv/bin/flake8 src/sensu_go tests
 	venv/bin/mypy --strict src/sensu_go
 
 .PHONY: unit

tests/unit/clients/http/test_base.py

@@ -57,23 +57,21 @@ def test_default(self, mocker):
         session_mock.return_value.verify is True
 
     def test_trailing_slash_removal(self, mocker):
-        session_mock = mocker.patch("requests.Session")
-
         client = DummyClient("https://my.url/")
 
         assert client.address == "https://my.url"
 
     def test_kill_verification(self, mocker):
         session_mock = mocker.patch("requests.Session")
 
-        client = DummyClient("https://my.url", verify=False)
+        DummyClient("https://my.url", verify=False)
 
         session_mock.return_value.verify is False
 
     def test_use_custom_ca_bundle_for_verification(self, mocker):
         session_mock = mocker.patch("requests.Session")
 
-        client = DummyClient("https://my.url", ca_path="some_path")
+        DummyClient("https://my.url", ca_path="some_path")
 
         session_mock.return_value.verify == "some_path"
 
@@ -91,7 +89,7 @@ def test_optional_parameter_combinations(
     ):
         session_mock = mocker.patch("requests.Session")
 
-        client = DummyClient("https://my.url", verify=verify, ca_path=ca_path)
+        DummyClient("https://my.url", verify=verify, ca_path=ca_path)
 
         session_mock.return_value.verify == verify_result
 
@@ -122,23 +120,23 @@ def test_right_method(self, requests_mock):
         client.get("/get/path")
 
 
-class TestHTTPClientGet:
+class TestHTTPClientPost:
     def test_right_method(self, requests_mock):
         requests_mock.post("https://my.url/post/path")
         client = DummyClient("https://my.url")
 
         client.post("/post/path", dict(post="data"))
 
 
-class TestHTTPClientGet:
+class TestHTTPClientPut:
     def test_right_method(self, requests_mock):
         requests_mock.put("https://my.url/put/path")
         client = DummyClient("https://my.url")
 
         client.put("/put/path", dict(put="data"))
 
 
-class TestHTTPClientGet:
+class TestHTTPClientDelete:
     def test_right_method(self, requests_mock):
         requests_mock.delete("https://my.url/delete/path")
         client = DummyClient("https://my.url")