Make nearley tool main testable and test it

lark/tools/nearley.py

@@ -169,17 +169,18 @@ def create_code_for_nearley_grammar(g, start, builtin_path, folder_path):
 
     return ''.join(emit_code)
 
-def main():
-    if len(sys.argv) < 3:
-        print("Reads Nearley grammar (with js functions) outputs an equivalent lark parser.")
-        print("Usage: %s <nearley_grammar_path> <start_rule> <nearley_lib_path>" % sys.argv[0])
-        return
-
-    fn, start, nearley_lib = sys.argv[1:]
+def main(fn, start, nearley_lib):
     with codecs.open(fn, encoding='utf8') as f:
         grammar = f.read()
     print(create_code_for_nearley_grammar(grammar, start, os.path.join(nearley_lib, 'builtin'), os.path.abspath(os.path.dirname(fn))))
 
 
 if __name__ == '__main__':
-    main()
+    if len(sys.argv) < 4:
+        print("Reads Nearley grammar (with js functions) outputs an equivalent lark parser.")
+        print("Usage: %s <nearley_grammar_path> <start_rule> <nearley_lib_path>" % sys.argv[0])
+        sys.exit(1)
+
+    fn, start, nearley_lib = sys.argv[1:]
+
+    main(fn, start, nearley_lib)

tests/test_nearley/test_nearley.py

@@ -8,10 +8,10 @@ import codecs
 
 logging.basicConfig(level=logging.INFO)
 
-from lark.tools.nearley import create_code_for_nearley_grammar
+from lark.tools.nearley import create_code_for_nearley_grammar, main as nearley_tool_main
 
-TEST_PATH    = os.path.dirname(__file__)
-NEARLEY_PATH = os.path.abspath(os.path.join(TEST_PATH, 'nearley'))
+TEST_PATH    = os.path.abspath(os.path.dirname(__file__))
+NEARLEY_PATH = os.path.join(TEST_PATH, 'nearley')
 BUILTIN_PATH = os.path.join(NEARLEY_PATH, 'builtin')
 
 class TestNearley(unittest.TestCase):
@@ -73,14 +73,7 @@ class TestNearley(unittest.TestCase):
 
     def test_utf8_2(self):
         fn = os.path.join(TEST_PATH, 'grammars/unicode.ne')
-        with codecs.open(fn, encoding='utf8') as f:
-            grammar = f.read()
-        code = create_code_for_nearley_grammar(grammar, 'main', BUILTIN_PATH, './')
-        d = {}
-        exec (code, d)
-        parse = d['parse']
-
-        parse(u'±a')
+        nearley_tool_main(fn, 'main', NEARLEY_PATH)
 
 
 if __name__ == '__main__':