Improve iop export public-key testing

* Improve wording of comments.
* Zeroize buffer before doing iop testing to
  avoid comparing with previous values in
  case they are not overwritten.
* Remove redundant testing.

Signed-off-by: Waleed Elmelegy <waleed.elmelegy@arm.com>
diff --git a/tf-psa-crypto/tests/suites/test_suite_psa_crypto.function b/tf-psa-crypto/tests/suites/test_suite_psa_crypto.function
index a793404..6be0f60 100644
--- a/tf-psa-crypto/tests/suites/test_suite_psa_crypto.function
+++ b/tf-psa-crypto/tests/suites/test_suite_psa_crypto.function
@@ -1929,7 +1929,7 @@
     }
 
     /* Adjust expected_status for interruptible export public-key.
-     * Interruptible export public-key is only supported for ECC key pairs and even
+     * Interruptible export public-key is only supported for ECC keys and even
      * for those only when MBEDTLS_ECP_RESTARTABLE is on.
      */
     if ((PSA_KEY_TYPE_IS_KEY_PAIR(type) || PSA_KEY_TYPE_IS_PUBLIC_KEY(type)) &&
@@ -1953,6 +1953,8 @@
         expected_export_status = PSA_ERROR_BAD_STATE;
     }
 
+    memset(exported, 0, export_size);
+
     do {
         status = psa_export_public_key_iop_complete(&export_key_operation,
                                                     exported,
@@ -1962,16 +1964,6 @@
     TEST_EQUAL(status, expected_export_status);
 
     if (status == PSA_SUCCESS) {
-        psa_key_type_t public_type = PSA_KEY_TYPE_PUBLIC_KEY_OF_KEY_PAIR(type);
-        size_t bits;
-        PSA_ASSERT(psa_get_key_attributes(key, &attributes));
-        bits = psa_get_key_bits(&attributes);
-        TEST_LE_U(expected_public_key->len,
-                  PSA_EXPORT_KEY_OUTPUT_SIZE(public_type, bits));
-        TEST_LE_U(expected_public_key->len,
-                  PSA_EXPORT_PUBLIC_KEY_OUTPUT_SIZE(public_type, bits));
-        TEST_LE_U(expected_public_key->len,
-                  PSA_EXPORT_PUBLIC_KEY_MAX_SIZE);
         TEST_MEMORY_COMPARE(expected_public_key->x, expected_public_key->len,
                             exported, exported_length);
     }