mergestate.commit: factor out making the list of records

Will aid in testing.

mercurial/merge.py

@@ -286,6 +286,11 b' class mergestate(object):'
     def commit(self):
         """Write current state on disk (if necessary)"""
         if self._dirty:
+            records = self._makerecords()
+            self._writerecords(records)
+            self._dirty = False
+
+    def _makerecords(self):
             records = []
             records.append(('L', hex(self._local)))
             records.append(('O', hex(self._other)))
@@ -297,8 +302,7 b' class mergestate(object):'
                     records.append(('D', '\0'.join([d] + v)))
                 else:
                     records.append(('F', '\0'.join([d] + v)))
-            self._writerecords(records)
-            self._dirty = False
+        return records
 
     def _writerecords(self, records):
         """Write current state on disk (both v1 and v2)"""