diff --git a/csst_ifs_sim/csst_ifs_sim.py b/csst_ifs_sim/csst_ifs_sim.py
index 15c1c2b82adc46fb023dce487ebbe0b7c24ea066..ba328abb7eb187db6e31a4995eb634a57f136952 100644
--- a/csst_ifs_sim/csst_ifs_sim.py
+++ b/csst_ifs_sim/csst_ifs_sim.py
@@ -4788,7 +4788,7 @@ if __name__ == "__main__":
     
     runIFSsim(sourcein, skyfitsin, configfile, 1, CSST_unittest, applyhole) 
  
-
+    return 1
     ############################################################################
     ############################################################################
     # it=range(1, exposureNum+1,1)
diff --git a/tests/test_ifs_sim.py b/tests/test_ifs_sim.py
index c8483a8d299ec9cb29187651a9af59ba4158981d..6522b679216214bd0099e7e055f512a110f1f07f 100644
--- a/tests/test_ifs_sim.py
+++ b/tests/test_ifs_sim.py
@@ -36,11 +36,12 @@ class TestDemoFunction(unittest.TestCase):
         
         print(dir_path)
         
+        d=0
         
-        csst_ifs_sim(dir_path)
+        d=csst_ifs_sim(dir_path)
         
         self.assertTrue(
-            1 == 1,
+            d == 1,
             "case 1: SCI sim passes.",
         )