Fix cache policy bug (#4789)

* Fix cache policy bug

* Fix test

panel/io/cache.py

@@ -239,7 +239,7 @@ def _cleanup_cache(cache, policy, max_items, time):
     their TTL (time-to-live) has expired.
     """
     while len(cache) >= max_items:
-        if policy.lower() == 'lifo':
+        if policy.lower() == 'fifo':
             key = list(cache.keys())[0]
         elif policy.lower() == 'lru':
             key = sorted(((k, time-t) for k, (_, _, _, t) in cache.items()),
@@ -329,6 +329,10 @@ def cache(
     cache_dir: str
         Directory to cache to on disk.
     """
+    if policy.lower() not in ('fifo', 'lru', 'lfu'):
+        raise ValueError(
+            f"Cache policy must be one of 'FIFO', 'LRU' or 'LFU', not {policy}."
+        )
 
     hash_funcs = hash_funcs or {}
     if func is None:

panel/tests/io/test_cache.py

@@ -201,12 +201,12 @@ def test_disk_cache():
 
 @pytest.mark.xdist_group("cache")
 @pytest.mark.parametrize('to_disk', (True, False))
-def test_cache_lifo(to_disk):
+def test_cache_fifo(to_disk):
     if to_disk and diskcache is None:
         pytest.skip('requires diskcache')
     global OFFSET
     OFFSET.clear()
-    fn = cache(function_with_args, max_items=2, policy='lifo', to_disk=to_disk)
+    fn = cache(function_with_args, max_items=2, policy='fifo', to_disk=to_disk)
     assert fn(0, 0) == 0
     assert fn(0, 1) == 1
     assert fn(0, 0) == 0