Adjust test case with invalid base64

Now that Base64 validates the number of trailing equals, adjust the PEM test
case that has a Base64 payload with a wrong number of trailing equals, where
`mbedtls_pem_read_buffer()` now returns a different error code. I'm not sure
what the exact intent of the test was, so add a variant with trailing equals
as well.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/tests/suites/test_suite_pem.function b/tests/suites/test_suite_pem.function
index 091cbd1..342ca52 100644
--- a/tests/suites/test_suite_pem.function
+++ b/tests/suites/test_suite_pem.function
@@ -15,16 +15,16 @@
 
 
     ret = mbedtls_pem_write_buffer(start, end, buf->x, buf->len, NULL, 0, &olen);
-    TEST_ASSERT(ret == MBEDTLS_ERR_BASE64_BUFFER_TOO_SMALL);
+    TEST_EQUAL(ret, MBEDTLS_ERR_BASE64_BUFFER_TOO_SMALL);
 
     check_buf = (unsigned char *) mbedtls_calloc(1, olen);
     TEST_ASSERT(check_buf != NULL);
 
     ret = mbedtls_pem_write_buffer(start, end, buf->x, buf->len, check_buf, olen, &olen2);
 
-    TEST_ASSERT(olen2 <= olen);
-    TEST_ASSERT(olen > strlen((char *) result_str));
-    TEST_ASSERT(ret == 0);
+    TEST_LE_U(olen2, olen);
+    TEST_LE_U(strlen((char *) result_str) + 1, olen);
+    TEST_EQUAL(ret, 0);
     TEST_ASSERT(strncmp((char *) check_buf, (char *) result_str, olen) == 0);
 
 exit:
@@ -76,15 +76,14 @@
 
     ret = mbedtls_pem_read_buffer(&ctx, header, footer, (unsigned char *) data,
                                   (unsigned char *) pwd, pwd_len, &use_len);
-    TEST_ASSERT(ret == res);
+    TEST_EQUAL(ret, res);
     if (ret != 0) {
         goto exit;
     }
 
     use_len = 0;
     buf = mbedtls_pem_get_buffer(&ctx, &use_len);
-    TEST_EQUAL(use_len, out->len);
-    TEST_ASSERT(memcmp(out->x, buf, out->len) == 0);
+    TEST_MEMORY_COMPARE(out->x, out->len, buf, use_len);
 
 exit:
     mbedtls_pem_free(&ctx);