b64_decode-test: Properly terminate strings before comparison

Undefined behavior in unit-tests is no fun.  assert_string_equal()
expects properly zero-terminated strings. None of the encoded test
strings contain a termination, hence add it manually.

Without this change, the test was often failing with a wrong error
message:

    [==========] tests_lib_b64_decode-test(tests): Running 1 test(s).
    [ RUN      ] test_b64_decode
    [  ERROR   ] --- "AB" != "AB"
    [   LINE   ] --- tests/lib/b64_decode-test.c:38: error: Failure!
    [  FAILED  ] test_b64_decode
    [==========] tests_lib_b64_decode-test(tests): 1 test(s) run.

Probably due to unprintable characters in the string. No idea why
my system is more susceptible to this issue.

Change-Id: Id1bd2c3ff06bc1d4e5aa21ddd0f1d5802540999d
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/84088
Reviewed-by: Jakub Czapiga <czapiga@google.com>
Reviewed-by: Nicholas Sudsgaard <devel+coreboot@nsudsgaard.com>
Reviewed-by: Paul Menzel <paulepanter@mailbox.org>
Reviewed-by: Matt DeVillier <matt.devillier@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/tests/lib/b64_decode-test.c b/tests/lib/b64_decode-test.c
index 189ce96237..8560eb2ccc 100644
--- a/tests/lib/b64_decode-test.c
+++ b/tests/lib/b64_decode-test.c
@@ -35,6 +35,9 @@ static void test_b64_decode(void **state)
 		res = b64_decode((uint8_t *)messages[i].enc, strlen(messages[i].enc), decoded);
 
 		assert_int_equal(res, (strlen(messages[i].dec)));
+
+		decoded[res] = 0x00;
+
 		assert_string_equal((const char *)decoded, messages[i].dec);
 
 		free(decoded);