add test code for multiple modifications

tests/unit_tests/test_mod_string.py

@@ -50,7 +50,7 @@ def test_internal_to_xisearch_carbamidomethylation_oxidation_dsso(self):
     def test_internal_to_xisearch_no_modification_dsso(self):
         """Test internal_to_xisearch_no_variable along with DSSO as crosslinker."""
         self.assertEqual(
-            mod.xisearch_to_internal("DSSO", "SNVPALEACPQKR", "IDGHMKK", "NAN", "NAN", "12", "6", "NaN", "NaN"),
+            mod.xisearch_to_internal("DSSO", "SNVPALEACPQKR", "IDGHMKK", "NaN", "NaN", "12", "6", "NaN", "NaN"),
             ("SNVPALEACPQK[UNIMOD:1896]R", "IDGHMK[UNIMOD:1896]K"),
         )
 
@@ -64,10 +64,17 @@ def test_internal_to_xisearch_carbamidomethylation_oxidation_dsbu(self):
     def test_internal_to_xisearch_no_modification_dsbu(self):
         """Test internal_to_xisearch_no_variable along with DSBU as crosslinker."""
         self.assertEqual(
-            mod.xisearch_to_internal("DSBU", "SNVPALEACPQKR", "IDGHMKK", "NAN", "NAN", "12", "6", "NaN", "NaN"),
+            mod.xisearch_to_internal("DSBU", "SNVPALEACPQKR", "IDGHMKK", "NaN", "NaN", "12", "6", "NaN", "NaN"),
             ("SNVPALEACPQK[UNIMOD:1884]R", "IDGHMK[UNIMOD:1884]K"),
         )
 
+    def test_internal_to_xisearch_double_modifications(self):
+        """Test internal_to_xisearch_double_variable."""
+        self.assertEqual(
+            mod.xisearch_to_internal("DSSO", "MKRM", "CKRC", "ox;ox", "cm;cm", "2", "2", "1;4", "1;4"),
+            ("M[UNIMOD:35]K[UNIMOD:1896]RM[UNIMOD:35]", "C[UNIMOD:4]K[UNIMOD:1896]RC[UNIMOD:4]"),
+        )
+
 
 class TestMaxQuantToInternal(unittest.TestCase):
     """Class to test MaxQuant to internal."""