LatestValueCache: Expose keys for which messages have been received

src/frequenz/channels/_latest_value_cache.py

@@ -44,6 +44,7 @@
 
 import asyncio
 import typing
+from collections.abc import Set
 
 from ._receiver import Receiver
 
@@ -145,6 +146,13 @@ def unique_id(self) -> str:
         """The unique identifier of this instance."""
         return self._unique_id
 
+    def keys(self) -> Set[HashableT]:
+        """Return the set of keys for which values have been received.
+
+        If no key function is provided, this will return an empty set.
+        """
+        return self._latest_value_by_key.keys()
+
     def get(self, key: HashableT | Sentinel = NO_KEY) -> T_co:
         """Return the latest value that has been received.
 

tests/test_latest_value_cache_integration.py

@@ -44,6 +44,8 @@ async def test_latest_value_cache() -> None:
 
     assert cache.get() == 19
 
+    assert cache.keys() == set()
+
 
 @pytest.mark.integration
 async def test_latest_value_cache_key() -> None:
@@ -59,6 +61,8 @@ async def test_latest_value_cache_key() -> None:
     with pytest.raises(ValueError, match="No value received for key: 0"):
         cache.get(0)
 
+    assert cache.keys() == set()
+
     await sender.send((5, "a"))
     await sender.send((6, "b"))
     await sender.send((5, "c"))
@@ -73,6 +77,8 @@ async def test_latest_value_cache_key() -> None:
     assert cache.get(5) == (5, "c")
     assert cache.get(6) == (6, "b")
 
+    assert cache.keys() == {5, 6}
+
     with pytest.raises(ValueError, match="No value received for key: 7"):
         cache.get(7)
 
@@ -92,3 +98,5 @@ async def test_latest_value_cache_key() -> None:
     await asyncio.sleep(0)
 
     assert cache.get(6) == (6, "g")
+
+    assert cache.keys() == {5, 6, 12}