test(msgraph): cover concurrent token cache reuse

tests/tools/test_microsoft_graph_auth.py

@@ -2,10 +2,13 @@
 
 from __future__ import annotations
 
+import asyncio
+
 import httpx
 import pytest
 
 from tools.microsoft_graph_auth import (
+    CachedAccessToken,
     DEFAULT_GRAPH_SCOPE,
     GraphCredentials,
     MicrosoftGraphConfigError,
@@ -66,6 +69,33 @@ class TestMicrosoftGraphTokenProvider:
         assert second == "token-1"
         assert len(calls) == 1
 
+    async def test_concurrent_calls_share_one_token_fetch(self):
+        calls: list[int] = []
+
+        provider = MicrosoftGraphTokenProvider(
+            GraphCredentials("tenant", "client", "secret"),
+        )
+
+        async def _fake_fetch():
+            calls.append(1)
+            await asyncio.sleep(0)
+            return CachedAccessToken(
+                access_token="token-1",
+                token_type="Bearer",
+                expires_at=9_999_999_999,
+            )
+
+        provider._fetch_access_token = _fake_fetch  # type: ignore[method-assign]
+
+        first, second = await asyncio.gather(
+            provider.get_access_token(),
+            provider.get_access_token(),
+        )
+
+        assert first == "token-1"
+        assert second == "token-1"
+        assert len(calls) == 1
+
     async def test_refreshes_when_cached_token_is_expired(self):
         calls: list[int] = []