tests: Refactor test_delayed_request_middleware.py

- Move expectation into parametrize
- Add newlines around assertions, to make it easier to scan for assertions
- Use simpler variable names if they are unambiguous (middleware, manager, actual)
- Remove extra f-string

tests/middlewares/test_delayed_request_middleware.py

@@ -8,36 +8,37 @@
 from tests import spider_with_crawler
 
 
-@pytest.mark.parametrize('meta', [
-    None,
-    {'wait_time': 1}
+@pytest.mark.parametrize('meta,expected', [
+    (None, type(None)),
+    ({'wait_time': 1}, Deferred),
 ])
-def test_middleware_output(meta):
+def test_middleware_output(meta, expected):
     spider = spider_with_crawler()
-    delay_middleware = DelayedRequestMiddleware()
-    request = Request(f'http://example.com', meta=meta)
-    returned_request = delay_middleware.process_request(request, spider)
-    if not meta:
-        assert returned_request is None
-    else:
-        assert isinstance(returned_request, Deferred)
+    middleware = DelayedRequestMiddleware()
+    request = Request('http://example.com', meta=meta)
+    actual = middleware.process_request(request, spider)
+
+    assert isinstance(actual, expected)
 
 
 def test_middleware_wait():
 
-    def mock_download_func(spider, request):
+    def download_func(spider, request):
         return request
 
     spider = spider_with_crawler()
-    downloader_manager = DownloaderMiddlewareManager.from_crawler(spider.crawler)
+    manager = DownloaderMiddlewareManager.from_crawler(spider.crawler)
     request = Request('http://example.com', meta={'wait_time': 1})
-    # we send the request to all the download middlewares including the delayed one
-    downloaded = downloader_manager.download(mock_download_func, request, spider)
+    # We send the request to all the downloader middlewares, including the delayed request middleware.
+    downloaded = manager.download(download_func, request, spider)
+
     assert isinstance(downloaded, Deferred)
+
     # https://github.com/scrapy/scrapy/blob/28262d4b241744aa7c090702db9a89411e3bbf9a/tests/test_downloadermiddleware.py#L36
     results = []
     downloaded.addBoth(results.append)
     test = TestCase()
     test._wait(downloaded)
-    returned_request = results[0]
-    assert returned_request.url == request.url
+
+    assert len(results) == 1
+    assert results[0].url == request.url