pythongh-109546: Add more tests for formatting floats (pythonGH-109548)

(cherry picked from commit beb5ec5)

Author: serhiy-storchaka

Lib/test/test_float.py

@@ -734,8 +734,13 @@ def test_format_testfile(self):
 
                 lhs, rhs = map(str.strip, line.split('->'))
                 fmt, arg = lhs.split()
-                self.assertEqual(fmt % float(arg), rhs)
-                self.assertEqual(fmt % -float(arg), '-' + rhs)
+                f = float(arg)
+                self.assertEqual(fmt % f, rhs)
+                self.assertEqual(fmt % -f, '-' + rhs)
+                if fmt != '%r':
+                    fmt2 = fmt[1:]
+                    self.assertEqual(format(f, fmt2), rhs)
+                    self.assertEqual(format(-f, fmt2), '-' + rhs)
 
     def test_issue5864(self):
         self.assertEqual(format(123.456, '.4'), '123.5')