New test helper to purge persistent key from memory

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/tests/include/test/psa_crypto_helpers.h b/tests/include/test/psa_crypto_helpers.h
index 9510c5f..3e356f9 100644
--- a/tests/include/test/psa_crypto_helpers.h
+++ b/tests/include/test/psa_crypto_helpers.h
@@ -43,6 +43,11 @@
  */
 void mbedtls_test_psa_purge_key_storage( void );
 
+/** Purge the in-memory cache of persistent keys recorded with
+ * #TEST_USES_KEY_ID.
+ */
+void mbedtls_test_psa_purge_key_cache( void );
+
 /** \def TEST_USES_KEY_ID
  *
  * Call this macro in a test function before potentially creating a