fix: handle InMemoryDatabase find_schemas latest when no versions ava…

…ilable for subject

karapace/in_memory_database.py

@@ -174,7 +174,7 @@ def find_schemas(self, *, include_deleted: bool, latest_only: bool) -> dict[Subj
             for subject, subject_data in self.subjects.items():
                 selected_schemas: list[SchemaVersion] = []
                 schemas = list(subject_data.schemas.values())
-                if latest_only:
+                if latest_only and len(schemas) > 0:
                     # TODO don't include the deleted here?
                     selected_schemas = [schemas[-1]]
                 else:

tests/unit/test_in_memory_database.py

@@ -0,0 +1,13 @@
+"""
+Copyright (c) 2024 Aiven Ltd
+See LICENSE for details
+"""
+from karapace.in_memory_database import InMemoryDatabase, Subject
+
+
+def test_find_schemas() -> None:
+    database = InMemoryDatabase()
+    subject = Subject("hello_world")
+    database.insert_subject(subject=subject)
+    expected = {subject: []}
+    assert database.find_schemas(include_deleted=True, latest_only=True) == expected