Fix issues with the right count of parsers used.

test/test_parser/test_fast_parser.py

@@ -61,24 +61,32 @@ def test_carriage_return_splitting():
 
 def test_change_and_undo():
 
-    def fp(src):
+    def fp(src, number_parsers_used):
         p = FastParser(load_grammar(), u(src))
         cache.save_parser(None, None, p, pickling=False)
 
         # TODO Don't change get_code, the whole thing should be the same.
         # -> Need to refactor the parser first, though.
         assert src == p.module.get_code()[:-1]
+        assert p.number_parsers_used == number_parsers_used
 
     cache.parser_cache.pop(None, None)
     func_before = 'def func():\n    pass\n'
-    fp(func_before + 'a')
-    fp(func_before + 'b')
-    fp(func_before + 'a')
-    fp(func_before + 'a')
+    # Parse the function and a.
+    fp(func_before + 'a', 2)
+    # Parse just b.
+    fp(func_before + 'b', 1)
+    # b has changed to a again, so parse that.
+    fp(func_before + 'a', 1)
+    # Same as before no parsers should be used.
+    fp(func_before + 'a', 0)
 
-    fp('a')
-    fp('b')
-    fp('a')
+    # Getting rid of an old parser: Still no parsers used.
+    fp('a', 0)
+    # Now the file has completely change and we need to parse.
+    fp('b', 1)
+    # And again.
+    fp('a', 1)
 
 
 def test_incomplete_function():