Fix test that wasn't actually effective

psa_destroy_key() returns success even if the slot is empty.
diff --git a/tests/suites/test_suite_pk.function b/tests/suites/test_suite_pk.function
index bf87b2b..37cf5c5 100644
--- a/tests/suites/test_suite_pk.function
+++ b/tests/suites/test_suite_pk.function
@@ -169,6 +169,7 @@
 
     /* test that freeing the context does not destroy the key */
     mbedtls_pk_free( &pk );
+    TEST_ASSERT( PSA_SUCCESS == psa_get_key_information( key, NULL, NULL ) );
     TEST_ASSERT( PSA_SUCCESS == psa_destroy_key( key ) );
 
 exit: