Fix CRLF optimal sequence bug

See #4.

I thought there'd be a more elegant fix here, but in the end I went with the
same one as inhttps://github.com/delimitry/pull/8/files#diff-bf7c11e2b0865687a2785c4fa2a55920d92137aa2b6548c5f87835d98f73339fR356-R357

aztec_code_generator.py

@@ -336,9 +336,10 @@ def find_optimal_sequence(data, encoding=None):
                 if last_mode == Mode.PUNCT:
                     last_c = cur_seq[x][-1]
                     if isinstance(last_c, int) and bytes((last_c, c)) in punct_2_chars:
-                        if cur_len[x] < next_len[x]:
-                            next_len[x] = cur_len[x]
-                            next_seq[x] = cur_seq[x][:-1] + [ bytes((last_c, c)) ]
+                        if x != Mode.MIXED:  # we need to avoid this because it contains '\r', '\n' individually, but not combined
+                            if cur_len[x] < next_len[x]:
+                                next_len[x] = cur_len[x]
+                                next_seq[x] = cur_seq[x][:-1] + [ bytes((last_c, c)) ]
         if len(next_seq[Mode.BINARY]) - 2 == 32:
             next_len[Mode.BINARY] += 11
         cur_len = next_len.copy()

test_aztec_code_generator.py

@@ -119,20 +119,19 @@ def test_find_optimal_sequence_bytes(self):
         self.assertEqual(find_optimal_sequence(b'@\xff'), b(Shift.BINARY, 2, '@', '\xff'))
         self.assertEqual(find_optimal_sequence(b'. @\xff'), b(Shift.PUNCT, '. ', Shift.BINARY, 2, '@', '\xff'))
 
-    @unittest.expectedFailure
     def test_find_optimal_sequence_CRLF_bug(self):
-        """ Demonstrate a known bug in find_optimal_sequence.
+        """ Demonstrate a known bug in find_optimal_sequence (https://github.com/dlenski/aztec_code_generator/pull/4)
 
         This is a much more minimal example of https://github.com/delimitry/aztec_code_generator/issues/7
 
         The string '\t<\r\n':
-          SHOULD be sequenced as:          Latch.MIXED '\t' < '\r' '\n'
-          but is incorrectly sequenced as: Latch.MIXED '\t' < '\r\n'
+          SHOULD be sequenced as:          Latch.MIXED '\t' Latch.PUNCT < '\r' '\n'
+          but is incorrectly sequenced as: Latch.MIXED '\t' Shift.PUNCT < '\r\n'
 
         ... which is impossible since no encoding of the 2 byte sequence b'\r\n' exists in MIXED mode. """
 
         self.assertEqual(find_optimal_sequence(b'\t<\r\n'), b(
-            Latch.MIXED, '\t', Shift.PUNCT, '<', '\r', '\n'
+            Latch.MIXED, '\t', Latch.PUNCT, '<', '\r\n'
         ))
 
     def test_optimal_sequence_to_bits(self):