test: Make CompletionResult a sequence

This should make pytest make niceer diffs when asserts fail,
specifically telling you what index the first not equal items were at.

Author: yedayak

test/t/conftest.py

@@ -7,6 +7,7 @@
 import sys
 import tempfile
 import time
+from collections.abc import Sequence
 from enum import Enum
 from pathlib import Path
 from types import TracebackType
@@ -753,7 +754,7 @@ def diff_env(before: List[str], after: List[str], ignore: str):
     assert not diff, "Environment should not be modified"
 
 
-class CompletionResult(Iterable[str]):
+class CompletionResult(Sequence[str]):
     """
     Class to hold completion results.
     """
@@ -773,6 +774,9 @@ def startswith(self, prefix: str) -> bool:
     def _items(self) -> List[str]:
         return sorted([x.strip() for x in self.output.strip().splitlines()])
 
+    def __getitem__(self, i) -> str:
+        return self._items()[i]
+
     def __eq__(self, expected: object) -> bool:
         """
         Returns True if completion contains expected items, and no others.
@@ -788,7 +792,7 @@ def __eq__(self, expected: object) -> bool:
             expiter = expected
         return self._items() == sorted(expiter)
 
-    def __contains__(self, item: str) -> bool:
+    def __contains__(self, item: object) -> bool:
         return item in self._items()
 
     def __iter__(self) -> Iterator[str]: