diff --git a/backend/pashub_fetcher/core_files.py b/backend/pashub_fetcher/core_files.py
index 3e69bf9a..050dde27 100644
--- a/backend/pashub_fetcher/core_files.py
+++ b/backend/pashub_fetcher/core_files.py
@@ -62,6 +62,12 @@ _MATCHERS: list[tuple[Callable[[str], bool], str]] = [
 ]
 
 
+def core_file_for(
+    filename: str, evidence_category: Optional[str] = None
+) -> Optional[CoreFiles]:
+    raise NotImplementedError
+
+
 def infer_file_type(filename: str) -> Optional[str]:
     for matcher, file_type in _MATCHERS:
         if matcher(filename):
diff --git a/backend/pashub_fetcher/tests/test_core_files.py b/backend/pashub_fetcher/tests/test_core_files.py
index 8bd31f15..5ac6b4f7 100644
--- a/backend/pashub_fetcher/tests/test_core_files.py
+++ b/backend/pashub_fetcher/tests/test_core_files.py
@@ -1,4 +1,4 @@
-from backend.pashub_fetcher.core_files import infer_file_type
+from backend.pashub_fetcher.core_files import CoreFiles, core_file_for, infer_file_type
 
 
 def test_infer_photopack():
@@ -81,3 +81,19 @@ def test_infer_retrofit_design_doc():
         infer_file_type("2603-OSM-B06M901-XX-DR-N-A_Alvaston Walk 022.pdf")
         == "retrofit_design_doc"
     )
+
+
+# ---------------------------------------------------------------------------
+# core_file_for
+# ---------------------------------------------------------------------------
+
+
+def test_core_file_for_evidence_category_returns_retrofit_design_doc() -> None:
+    # Arrange
+    filename = "2512-OSM-H21M900-XX-DR-N-A_Lord Nelson Street 018.pdf"
+
+    # Act
+    result = core_file_for(filename, evidence_category="retrofit design")
+
+    # Assert
+    assert result == CoreFiles.RETROFIT_DESIGN_DOC