tests: Add more tests to improve coverage, mostly testing exceptions.

tests/basics/string_format.py

@@ -123,4 +123,74 @@ if full_tests:
                     for str in ('', 'a', 'bcd', 'This is a test with a longer string'):
                         test_fmt(conv, fill, alignment, '', '', width, '', 's', str)
 
-# TODO Add tests for erroneous format strings.
+# tests for errors in format string
+
+try:
+    '{0:0}'.format('zzz')
+except (ValueError):
+    print('ValueError')
+
+try:
+    '{1:}'.format(1)
+except IndexError:
+    print('IndexError')
+
+try:
+    '}'.format('zzzz')
+except ValueError:
+    print('ValueError')
+
+try:
+    'abc{!d}'.format('1')
+except ValueError:
+    print('ValueError')
+
+try:
+    '{abc'.format('zzzz')
+except ValueError:
+    print('ValueError')
+
+try:
+    '{!s :}'.format(2)
+except ValueError:
+    print('ValueError')
+
+try:
+    '{}{0}'.format(1, 2)
+except ValueError:
+    print('ValueError')
+
+try:
+    '{1:}'.format(1)
+except IndexError:
+    print('IndexError')
+
+try:
+    '{ 0 :*^10}'.format(12)
+except KeyError:
+    print('KeyError')
+
+try:
+    '{0}{}'.format(1)
+except ValueError:
+    print('ValueError')
+
+try:
+    '{}{}'.format(1)
+except IndexError:
+    print('IndexError')
+
+try:
+    '{0:+s}'.format('1')
+except ValueError:
+    print('ValueError')
+
+try:
+    '{0:+c}'.format(1)
+except ValueError:
+    print('ValueError')
+
+try:
+    '{0:s}'.format(1)
+except ValueError:
+    print('ValueError')