test: add extra test case

Author: AbduazizZiyodov

src/trio/_tests/test_sync.py

@@ -237,8 +237,25 @@ async def test_CapacityLimiter_zero_limit_tokens() -> None:
         c.total_tokens = 1
         assert c.statistics().tasks_waiting == 0
         assert c.statistics().borrowers == [6]
-
         c.release_on_behalf_of(6)
+
+        await c.acquire_on_behalf_of(0)  # total_tokens is 1
+
+        nursery.start_soon(c.acquire_on_behalf_of, 1)
+        c.total_tokens = 0
+
+        assert c.statistics().borrowers == [0]
+
+        c.release_on_behalf_of(0)
+        assert c.statistics().borrowers == []
+        assert c.statistics().tasks_waiting == 0
+
+        c.total_tokens = 1
+        await wait_all_tasks_blocked()
+        assert c.statistics().borrowers == [1]
+
+        c.release_on_behalf_of(1)
+
         c.total_tokens = 0
 
         nursery.cancel_scope.cancel()