tests: Kill off find_one() helper.

This was only recently added.  Using tuple
assignment raises the same errors, so the
indirection probably isn't worth it.

zerver/lib/test_classes.py

@@ -1,7 +1,7 @@
 from contextlib import contextmanager
 from email.utils import parseaddr
 from fakeldap import MockLDAP
-from typing import (cast, Any, Callable, Dict, Iterable,
+from typing import (cast, Any, Dict, Iterable,
                     Iterator, List, Optional,
                     Tuple, Union, Set)
 
@@ -821,40 +821,6 @@ class ZulipTestCase(TestCase):
             r for r in data
             if r['id'] == db_id][0]
 
-    def find_one(self,
-                 lst: List[Any],
-                 predicate: Callable[[Any], bool],
-                 member_name: str) -> Any:
-        matches = [
-            item for item in lst
-            if predicate(item)
-        ]
-
-        if len(matches) == 1:
-            # Happy path!
-            return matches[0]
-
-        if True:  # nocoverage
-            print('\nERROR: findOne fails on this list:\n')
-            print('[')
-
-            for item in lst:
-                print('   ', item, ',')
-
-            print(']')
-
-            if len(matches) == 0:
-                raise ValueError(
-                    'No matches: {}'.format(member_name)
-                )
-
-            raise ValueError(
-                'Too many matches ({}): {}'.format(
-                    len(matches),
-                    member_name
-                )
-            )
-
     def init_default_ldap_database(self) -> None:
         """
         Takes care of the mock_ldap setup, loads

zerver/tests/test_users.py

@@ -1451,11 +1451,10 @@ class GetProfileTest(ZulipTestCase):
         result = self.api_get(hamlet, "/api/v1/users")
         self.assert_json_success(result)
 
-        my_user = self.find_one(
-            result.json()['members'],
-            lambda user: user['email'] == hamlet.email,
-            'member for Hamlet'
-        )
+        (my_user,) = [
+            user for user in result.json()['members']
+            if user['email'] == hamlet.email
+        ]
 
         self.assertEqual(
             my_user['avatar_url'],