Revert "test_helpers: Fix a nonexistent import."

This reverts commit fa18913b8b.

We fix the typo when doing this, though.

mypy.ini

@@ -57,6 +57,9 @@ ignore_missing_imports = True
 [mypy-lister,.lister]
 ignore_missing_imports = True
 
+[mypy-zerver.lib.test_case]
+ignore_missing_imports = True
+
 
 # Our own libraries, maintained outside this repo and installed
 # through pip.  We need to tell mypy where to find them.

zerver/lib/test_helpers.py

@@ -46,7 +46,9 @@ from zerver.models import (
 )
 
 from zerver.lib.request import JsonableError
-from zerver.lib.test_classes import ZulipTestCase
+
+if False:
+    from zerver.lib.test_classes import ZulipTestCase
 
 import collections
 import base64
@@ -289,7 +291,7 @@ def instrument_url(f: UrlFuncT) -> UrlFuncT:
     if not INSTRUMENTING:  # nocoverage -- option is always enabled; should we remove?
         return f
     else:
-        def wrapper(self: ZulipTestCase, url: str, info: Dict[str, Any]={},
+        def wrapper(self: 'ZulipTestCase', url: str, info: Dict[str, Any]={},
                     **kwargs: Any) -> HttpResponse:
             start = time.time()
             result = f(self, url, info, **kwargs)