Add concurrent/multi-threaded tests for thread-safety verification

Closes #50

Adds four new tests exercising simultaneous get/set/delete/clear
operations from multiple threads on shared Storage and Cache instances,
including scenarios with an active TTL expiration thread.

Made-with: Cursor

Author: fabien-marty

tests/test_cache.py

@@ -1,4 +1,5 @@
 import time
+from concurrent.futures import ThreadPoolExecutor, as_completed
 from typing import Any, cast
 
 import pytest
@@ -381,3 +382,65 @@ def test_cache_default_ttl_sentinel():
 
     time.sleep(0.2)
     assert cache.get("key2") == "value2"  # Should still be there
+
+
+def test_cache_concurrent_get_set_delete_clear():
+    """Multiple threads performing mixed operations on a shared Cache must not raise exceptions."""
+    num_threads = 10
+    num_operations = 200
+    cache = Cache(
+        max_items=50,
+        size_limit_in_bytes=None,
+        default_ttl=None,
+        expiration_thread_max_checks_per_iteration=0,
+    )
+
+    def worker(thread_id: int) -> None:
+        for i in range(num_operations):
+            key = f"key{i % 20}"
+            op = (thread_id * num_operations + i) % 4
+            if op == 0:
+                cache.set(key, f"value-{thread_id}-{i}")
+            elif op == 1:
+                result = cache.get(key)
+                assert result is CACHE_MISS or isinstance(result, str)
+            elif op == 2:
+                cache.delete(key)
+            else:
+                cache.clear()
+
+    with ThreadPoolExecutor(max_workers=num_threads) as executor:
+        futures = [executor.submit(worker, t) for t in range(num_threads)]
+        for future in as_completed(futures):
+            future.result()
+
+    assert cache.number_of_items <= 50
+    cache.close()
+
+
+def test_cache_concurrent_with_ttl():
+    """Concurrent Cache access with TTL expiration thread active must not corrupt state."""
+    num_threads = 8
+    num_operations = 100
+    cache = Cache(
+        max_items=100,
+        default_ttl=0.05,
+        expiration_thread_delay=0.01,
+        expiration_thread_max_checks_per_iteration=50,
+    )
+
+    def worker(thread_id: int) -> None:
+        for i in range(num_operations):
+            key = f"key{i % 10}"
+            if i % 2 == 0:
+                cache.set(key, f"v{thread_id}-{i}")
+            else:
+                result = cache.get(key)
+                assert result is CACHE_MISS or isinstance(result, str)
+
+    with ThreadPoolExecutor(max_workers=num_threads) as executor:
+        futures = [executor.submit(worker, t) for t in range(num_threads)]
+        for future in as_completed(futures):
+            future.result()
+
+    cache.close(wait=True)

tests/test_storage.py

@@ -1,5 +1,6 @@
 import random
 import time
+from concurrent.futures import ThreadPoolExecutor, as_completed
 
 import pytest
 
@@ -310,6 +311,65 @@ def test_overwrite_existing_key_size_tracking():
     storage.close()
 
 
+def test_storage_concurrent_get_set_delete():
+    """Multiple threads performing get/set/delete on a shared Storage must not raise exceptions."""
+    num_threads = 10
+    num_operations = 200
+    storage = Storage[bytes](
+        size_limit_in_bytes=None,
+        max_items=50,
+        expiration_thread_max_checks_per_iteration=0,
+    )
+
+    def worker(thread_id: int) -> None:
+        for i in range(num_operations):
+            key = f"key{i % 20}"
+            op = (thread_id * num_operations + i) % 3
+            if op == 0:
+                storage.set(key, f"value-{thread_id}-{i}".encode())
+            elif op == 1:
+                storage.get(key)
+            else:
+                storage.delete(key)
+
+    with ThreadPoolExecutor(max_workers=num_threads) as executor:
+        futures = [executor.submit(worker, t) for t in range(num_threads)]
+        for future in as_completed(futures):
+            future.result()
+
+    assert storage.number_of_items <= 50
+    storage.close()
+
+
+def test_storage_concurrent_with_ttl():
+    """Concurrent get/set with a live expiration thread must not corrupt state."""
+    num_threads = 8
+    num_operations = 100
+    storage = Storage[bytes](
+        size_limit_in_bytes=None,
+        max_items=100,
+        default_ttl=0.05,
+        expiration_thread_delay=0.01,
+        expiration_thread_max_checks_per_iteration=50,
+    )
+
+    def worker(thread_id: int) -> None:
+        for i in range(num_operations):
+            key = f"key{i % 10}"
+            if i % 2 == 0:
+                storage.set(key, f"v{thread_id}-{i}".encode())
+            else:
+                result = storage.get(key)
+                assert result is CACHE_MISS or isinstance(result, bytes)
+
+    with ThreadPoolExecutor(max_workers=num_threads) as executor:
+        futures = [executor.submit(worker, t) for t in range(num_threads)]
+        for future in as_completed(futures):
+            future.result()
+
+    storage.close(wait=True)
+
+
 def test_clear():
     """Test that clear() removes all items and resets size tracking."""
     storage = Storage[bytes](