TST: Extend unittest for empty diff by id

unittests/test_apiutils.py

@@ -466,6 +466,15 @@ def test_empty_diff():
     assert not empty_diff(rec_a, rec_b)
     assert empty_diff(rec_a, rec_b, compare_referenced_records=True)
 
+    # special case of ids
+    rec_a = db.Record(id=12)
+    rec_b = db.Record()
+    assert not empty_diff(rec_a, rec_b)
+    rec_b.id = 13
+    assert not empty_diff(rec_a, rec_b)
+    rec_b.id = 12
+    assert empty_diff(rec_a, rec_b)
+
 
 def test_force_merge():
     """Test whether a forced merge overwrites existing properties correctly."""