Update README with testing instructions for TTL

README.md

@@ -299,6 +299,33 @@ If performance matters to you:
    has been made to make the performance impact minimal, but it
    isn't nothing.
 
+## Testing
+
+When writing tests that involve TTL-related functionality, note that
+this module creates an internal reference to the global
+`performance` or `Date` objects at import time. If you import it
+statically at the top level, those references cannot be mocked or
+overridden in your test environment.
+
+To avoid this, dynamically import the package within your tests so
+that the references are captured after your mocks are applied. For
+example:
+
+```js
+// ❌ Not recommended
+import { LRUCache } from 'lru-cache'
+// mocking timers, e.g. jest.useFakeTimers()
+
+// ✅ Recommended for TTL tests
+// mocking timers, e.g. jest.useFakeTimers()
+const { LRUCache } = await import('lru-cache')
+```
+
+This ensures that your mocked timers or time sources are respected
+when testing TTL behavior.
+
+
+
 ## Breaking Changes in Version 7
 
 This library changed to a different algorithm and internal data