Increase test coverage for string formatting

[manoj-marimuthu]

In Lib/test/test_str.py, string formatting is tested for nan and inf but not for -inf. -inf could be the most important among them (since we have to check if '-' formats correctly).

current test cases:

self.assertEqual('%f' % NAN, 'nan')
self.assertEqual('%F' % NAN, 'NAN')
self.assertEqual('%f' % INF, 'inf')
self.assertEqual('%F' % INF, 'INF')
self.assertEqual('%f' % -INF, '-inf')
self.assertEqual('%F' % -INF, '-INF')

Linked PRs

• gh-151162: Increase test coverage for string formatting #151161