It seems that some assertions in Lib/test/test_unicode.py:UnicodeTest.test_format_map do not implement their intent e.g.,

        self.assertRaises(TypeError, '{'.format_map)
        self.assertRaises(TypeError, '}'.format_map)
        self.assertRaises(TypeError, 'a{'.format_map)
        self.assertRaises(TypeError, 'a}'.format_map)
        self.assertRaises(TypeError, '{a'.format_map)
        self.assertRaises(TypeError, '}a'.format_map)

The intent might be to test:

  >>> '{'.format_map({})
  Traceback (most recent call last):
    File "<stdin>", line 1, in <module>
  ValueError: Single '{' encountered in format string

But it actually tests:

  >>> '{'.format_map()
  Traceback (most recent call last):
    File "<stdin>", line 1, in <module>
  TypeError: format_map() takes exactly one argument (0 given)

Provided correct-assertions-in-test_format_map.patch contains additional assertions e.g.,

      self.assertRaises(ValueError, '{'.format_map, {})

Old assertions might be useful so they're left untouched.

I don't think the existing tests have any value. I might leave one of them, but I think I'll just use your new tests instead.

akira: I'd like to add your name to the Misc/ACKS file, if it's not already there. What's your full name?

Thanks for the bug report and patch.

TypeError tests can check that an implementation raises a correct exception type i.e., it doesn't raise ValueError prematurely on invalid format_string without checking that there is mapping argument.

METH_O does it for CPython. I'm not sure how other implementations might behave.

eric: I'd read http://docs.python.org/devguide/patch.html#preparation but I thought 4 lines are not worth it to change Misc/ACKS. Full pseudonym: Akira Li

When someone puts thought into a report or patch, they deserve to be in Misc/ACKS.  Just noticing one typo doesn’t qualify, but pretty much anything above does.  :)

New changeset 995cddd15313 by Eric V. Smith in branch '3.2':
str.format_map tests don't do what they say: fix to actually implement the intent of the test. Closes #13450.
http://hg.python.org/cpython/rev/995cddd15313

New changeset 0df295d590a8 by Eric V. Smith in branch 'default':
str.format_map tests don't do what they say: fix to actually implement the intent of the test. Closes #13450. Patch by Akira Li.
http://hg.python.org/cpython/rev/0df295d590a8