diff --git a/Lib/tabnanny.py b/Lib/tabnanny.py
--- a/Lib/tabnanny.py
+++ b/Lib/tabnanny.py
@@ -19,30 +19,29 @@ releases; such changes may not be backwa
 # XXX script-like.  This will be addressed later.
 
 __version__ = "6"
 
 import os
 import sys
 import getopt
 import tokenize
-if not hasattr(tokenize, 'NL'):
-    raise ValueError("tokenize.NL doesn't exist -- tokenize module too old")
 
 __all__ = ["check", "NannyNag", "process_tokens"]
 
 verbose = 0
 filename_only = 0
 
 def errprint(*args):
     sep = ""
     for arg in args:
         sys.stderr.write(sep + str(arg))
         sep = " "
     sys.stderr.write("\n")
+    sys.exit(1)
 
 def main():
     global verbose, filename_only
     try:
         opts, args = getopt.getopt(sys.argv[1:], "qv")
     except getopt.error as msg:
         errprint(msg)
         return
diff --git a/Lib/test/bad_indentation_1.py b/Lib/test/bad_indentation_1.py
new file mode 100644
--- /dev/null
+++ b/Lib/test/bad_indentation_1.py
@@ -0,0 +1,3 @@
+def spam(eggs):
+    if eggs == 42:
+	  return True
diff --git a/Lib/test/test_tabnanny.py b/Lib/test/test_tabnanny.py
new file mode 100644
--- /dev/null
+++ b/Lib/test/test_tabnanny.py
@@ -0,0 +1,47 @@
+import unittest
+
+from test import support, script_helper
+
+
+class CommandLineTest(unittest.TestCase):
+
+    def tabnannycmd(self, *args, expected_success=True):
+        if expected_success:
+            run_cmd = script_helper.assert_python_ok
+        else:
+            run_cmd = script_helper.assert_python_failure
+        rc, out, err = run_cmd('-m', 'tabnanny', *args)
+        return out if not rc else err
+
+    def test_mix_of_tabs_and_spaces(self):
+        badfile = support.findfile('bad_indentation_1.py')
+        out = self.tabnannycmd(badfile)
+        self.assertIn(b"3 '\\t  return True\\n'\n", out)
+
+    def test_mix_of_tabs_and_spaces_verbose(self):
+        badfile = support.findfile('bad_indentation_1.py')
+        out = self.tabnannycmd('-v', badfile)
+        self.assertIn(b"*** Line 3: trouble in tab city! ***\noffending line: '\\t  return True\\n'", out)
+        # more verbose
+        out = self.tabnannycmd('-vv', badfile)
+        self.assertTrue(out.startswith(b"checking"))
+        self.assertIn(b"*** Line 3: trouble in tab city! ***\noffending line: '\\t  return True\\n'", out)
+
+    def test_quiet_flag(self):
+        badfile = support.findfile('bad_indentation_1.py')
+        out = self.tabnannycmd('-q', badfile)
+        self.assertEqual(badfile.encode('ascii') + b'\n', out)
+
+    def test_success(self):
+        goodfile = support.findfile('gdb_sample.py')
+        out = self.tabnannycmd(goodfile)
+        self.assertEqual(b'', out)
+
+    def test_usage(self):
+        libtabnanny = support.findfile('tabnanny.py')
+        out = self.tabnannycmd(expected_success=False)
+        expected = b'Usage: ' + libtabnanny.encode('ascii') + b' [-v] file_or_directory ...'
+        self.assertEqual(expected, out)
+
+if __name__ == '__main__':
+    unittest.main()