diff -r 2c37f9dabc32 -r f4433f2713d0 tests/test-encoding-func.py
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/tests/test-encoding-func.py	Sun Apr 23 12:59:42 2017 +0900
@@ -0,0 +1,33 @@
+from __future__ import absolute_import
+
+import unittest
+
+from mercurial import (
+    encoding,
+)
+
+class IsasciistrTest(unittest.TestCase):
+    asciistrs = [
+        b'a',
+        b'ab',
+        b'abc',
+        b'abcd',
+        b'abcde',
+        b'abcdefghi',
+        b'abcd\0fghi',
+    ]
+
+    def testascii(self):
+        for s in self.asciistrs:
+            self.assertTrue(encoding.isasciistr(s))
+
+    def testnonasciichar(self):
+        for s in self.asciistrs:
+            for i in range(len(s)):
+                t = bytearray(s)
+                t[i] |= 0x80
+                self.assertFalse(encoding.isasciistr(bytes(t)))
+
+if __name__ == '__main__':
+    import silenttestrunner
+    silenttestrunner.main(__name__)