diff --git a/tests/test_parser.py b/tests/test_parser.py
index 8d14146f..aac8d242 100644
--- a/tests/test_parser.py
+++ b/tests/test_parser.py
@@ -92,7 +92,7 @@ def test_auto_design_generation_fromxlsgainmode(xls_input, expected_json_output)
     build_network(network, equipment, p_db, p_total_db)
     save_network(xls_input, network)
 
-    actual_json_output = f'{str(xls_input)[0:len(str(xls_input))-4]}_auto_design.json'
+    actual_json_output = xls_input.with_name(xls_input.stem + '_auto_design').with_suffix('.json')
 
     with open(actual_json_output, encoding='utf-8') as f:
         actual = load(f)
@@ -132,7 +132,7 @@ def test_auto_design_generation_fromjson(json_input, expected_json_output):
     build_network(network, equipment, p_db, p_total_db)
     save_network(json_input, network)
 
-    actual_json_output = f'{str(json_input)[0:len(str(json_input))-5]}_auto_design.json'
+    actual_json_output = json_input.with_name(json_input.stem + '_auto_design').with_suffix('.json')
 
     with open(actual_json_output, encoding='utf-8') as f:
         actual = load(f)
@@ -159,7 +159,7 @@ def test_excel_service_json_generation(xls_input, expected_json_output):
     """
     convert_service_sheet(xls_input, eqpt_filename)
 
-    actual_json_output = f'{str(xls_input)[:-4]}_services.json'
+    actual_json_output = xls_input.with_name(xls_input.stem + '_services').with_suffix('.json')
     with open(actual_json_output, encoding='utf-8') as f:
         actual = load(f)
     unlink(actual_json_output)