TST: Add test for multiple circular macro definitions

unittests/test_macros.py

@@ -249,3 +249,38 @@ testnode:
     assert dat["testnode"]["obl"]["replaced1"]["c"]["t2"] == "25"
     assert dat["testnode"]["obl"]["replaced1"]["d"][0] == "a"
     assert dat["testnode"]["obl"]["replaced1"]["d"][1] == "25"
+
+
+def test_circular_macro_definition(register_macros, macro_store_reset):
+    """Test the (ab-)use of macros to create an infinite loop."""
+    cfood = _temp_file_load("""
+---
+metadata:
+  macros:
+    - !defmacro
+      name: test_one
+      params: {}
+      definition: !macro
+        test_two:
+    - !defmacro
+      name: test_two
+      params: {}
+      definition: !macro
+        test_one:
+    - !defmacro
+      name: test_three
+      params: {}
+      definition: !macro
+        test_two:
+---
+extroot: !macro
+  test_one:
+extroot2: !macro
+  test_three:
+    """)
+    # macros in macros can be used, but there are no circles; they stop at the first one.
+    assert "test_one" not in cfood["extroot"]
+    assert cfood["extroot"]["test_two"] is None
+    assert "test_three" not in cfood["extroot2"]
+    assert "test_one" not in cfood["extroot2"]
+    assert cfood["extroot2"]["test_two"] is None