Fixes MRO serial issue

plio/io/isis_serial_number.py

@@ -82,6 +82,7 @@ def generate_serial_number(label):
 
     # Sort the keys to ensure proper iteration order
     keys = sorted(translation.keys())
+
     for k in keys:
         try:
             group = translation[k]

plio/io/tests/test_isis_serial_numbers.py

 import os
 import sys
-import unittest
 
-from plio.examples import get_path
-
-sys.path.insert(0, os.path.abspath('..'))
+import pytest
 
 from plio.io import isis_serial_number
+from plio.examples import get_path
+
+@pytest.fixture
+def apollo_lbl():
+    return get_path('Test_PVL.lbl')
 
+@pytest.fixture
+def ctx_lbl():
+    return get_path('ctx.pvl')
 
-class TestIsisSerials(unittest.TestCase):
+@pytest.mark.parametrize("label, expected", [(apollo_lbl(), 'APOLLO15/METRIC/1971-07-31T14:02:27.179'),
+                                             (ctx_lbl(),'MRO/CTX/0906095311:038')
+                                             ])
+def test_generate_serial_number(label, expected):
+    serial = isis_serial_number.generate_serial_number(label)
+    assert serial == expected
 
-    def test_generate_serial_number(self):
-        label = get_path('Test_PVL.lbl')
-        serial = isis_serial_number.generate_serial_number(label)
-        self.assertEqual('APOLLO15/METRIC/1971-07-31T14:02:27.179', serial)
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+    
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