Add testcase for maximum padding length

Signed-off-by: David Horstmann <david.horstmann@arm.com>
diff --git a/tests/suites/test_suite_cipher.padding.data b/tests/suites/test_suite_cipher.padding.data
index bd04a50..85b14c1 100644
--- a/tests/suites/test_suite_cipher.padding.data
+++ b/tests/suites/test_suite_cipher.padding.data
@@ -224,6 +224,9 @@
 Constant-time PKCS7 padding, valid #2
 get_pkcs_padding:"00112233445566778899AA0505050505":0:11
 
+Constant-time PKCS7 padding, valid #3
+get_pkcs_padding:"10101010101010101010101010101010":0:0
+
 Constant-time PKCS7 padding, invalid zero
 get_pkcs_padding:"00112233445566778899AABBCCDDEE00":MBEDTLS_ERR_CIPHER_INVALID_PADDING:0