diff --git a/petabtests/__init__.py b/petabtests/__init__.py
index 863c429..ae75034 100644
--- a/petabtests/__init__.py
+++ b/petabtests/__init__.py
@@ -6,3 +6,4 @@
 from .file import *  # noqa: F403, F401
 from .evaluate import *  # noqa: F403, F401
 from .core import *  # noqa: F403, F401
+from .antimony import *  # noqa: F403, F401
diff --git a/petabtests/antimony.py b/petabtests/antimony.py
index 21b31a7..73c649e 100644
--- a/petabtests/antimony.py
+++ b/petabtests/antimony.py
@@ -3,6 +3,8 @@
 import antimony as ant
 from pathlib import Path
 
+__all__ = ["antimony_to_sbml_str"]
+
 
 def antimony_to_sbml_str(ant_model: str | Path) -> str:
     """Convert Antimony string to SBML model.
diff --git a/petabtests/cases/v1.0.0/sbml/0018/0018.py b/petabtests/cases/v1.0.0/sbml/0018/0018.py
index 747ca78..853a30f 100644
--- a/petabtests/cases/v1.0.0/sbml/0018/0018.py
+++ b/petabtests/cases/v1.0.0/sbml/0018/0018.py
@@ -3,8 +3,12 @@
 import pandas as pd
 from petab.v1.C import *
 from pathlib import Path
-from petabtests import PetabTestCase, analytical_a, analytical_b
-from petabtests.antimony import antimony_to_sbml_str
+from petabtests import (
+    PetabTestCase,
+    analytical_a,
+    analytical_b,
+    antimony_to_sbml_str,
+)
 
 DESCRIPTION = cleandoc("""
 ## Objective
@@ -39,9 +43,7 @@
     k1 = 0
     k2 = 0
     compartment default_compartment
-    species A in default_compartment = 0
-    B = 0
-    A = a0
+    species A in default_compartment = a0
     B = b0
     A' = k2 * B - k1 * A
     B' = - default_compartment * k2 * B + default_compartment * k1 * A
diff --git a/petabtests/cases/v2.0.0/sbml/0018/0018.py b/petabtests/cases/v2.0.0/sbml/0018/0018.py
index 3e84944..2b3586f 100644
--- a/petabtests/cases/v2.0.0/sbml/0018/0018.py
+++ b/petabtests/cases/v2.0.0/sbml/0018/0018.py
@@ -3,8 +3,12 @@
 import pandas as pd
 from petab.v1.C import *
 from pathlib import Path
-from petabtests import PetabTestCase, analytical_a, analytical_b
-from petabtests.antimony import antimony_to_sbml_str
+from petabtests import (
+    PetabTestCase,
+    analytical_a,
+    analytical_b,
+    antimony_to_sbml_str,
+)
 
 DESCRIPTION = cleandoc("""
 ## Objective