Experimental lexer generator: Clarify TransitionKeys.disjoint_keys.

tools/lexer_generator/transition_key_test.py

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@@ skipping 59 matching lines @@
         for c in no_match:
           self.assertEqual(invert, key.matches_char(c))
 
   def test_self_defined_classes(self):
     graph = RegexParser.parse("[a-z]")
     classes = {
       'self_defined' : TransitionKey.character_class(graph, {})}
     graph = RegexParser.parse("[^:self_defined:]")
     key = TransitionKey.character_class(graph, classes)
     self.assertTrue(key.matches_char('A'))
+
+
+  def test_disjoint_keys(self):
+    key1 = TransitionKey([(1, 10)])
+    key2 = TransitionKey([(5, 15)])
+    disjoint_set = TransitionKey.disjoint_keys(set([key1, key2]))
+    self.assertTrue(TransitionKey([(1, 4)]) in disjoint_set)
+    self.assertTrue(TransitionKey([(5, 10)]) in disjoint_set)
+    self.assertTrue(TransitionKey([(11, 15)]) in disjoint_set)