diff --git a/src/caoscrawler/transformer_functions.py b/src/caoscrawler/transformer_functions.py
index 842c4c0986deff51908a79f4cd2d7c4c5ecc3e56..b68c9f64d9f2da8b1d51d35598c579bfee7511ab 100644
--- a/src/caoscrawler/transformer_functions.py
+++ b/src/caoscrawler/transformer_functions.py
@@ -4,5 +4,12 @@
 
 from typing import Any
 
+import re
+
 def ifelse(in_value: Any, in_parameters: dict):
-    raise NotImplementedError()
+    if "match" not in in_parameters or "then" not in in_parameters:
+        raise RuntimeError("Mandatory parameters missing.")
+    
+    if re.match(in_parameters["match"], in_value) is not None:
+        return in_parameters["then"]
+    return in_value
diff --git a/unittests/test_transformers.py b/unittests/test_transformers.py
index 9df450ee9c1c7997a5e1c0a4e8783bf31c8cd604..c7cfe030f9b424db7de946cd3c0f4f4c74d4c822 100644
--- a/unittests/test_transformers.py
+++ b/unittests/test_transformers.py
@@ -59,14 +59,18 @@ def test_simple_transformer():
     records = scan_directory(UNITTESTDIR / "test_directories" / "test_transformers",
                              UNITTESTDIR / "test_directories" / "test_transformers" /
                              "cfood.yml")
-    breakpoint()
+    
     for r in records:
         assert r.get_property("Day") is not None
         assert r.get_property("DayShort") is not None
         assert r.get_property("DayShort").value != "$day_short"
         if r.get_property("DayShort").value == "Unk":
             # This unkown folder should not lead to a replacement
-            assert r.get_property("Day").value == "$day_long"
+            assert r.get_property("Day").value == "Unk"
+        elif r.get_property("DayShort").value == "Mon":
+            assert r.get_property("Day").value == "Monday"
+        elif r.get_property("DayShort").value == "Tue":
+            assert r.get_property("Day").value == "Tuesday"
         else:
             assert r.get_property("Day").value != "$day_long"