Create a separate test module for PSA exercise_key

The code will be moved in a subsequent commit.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

tests/include/test/psa_exercise_key.h

@@ -0,0 +1,30 @@
+/** Code to exercise a PSA key object, i.e. validate that it seems well-formed
+ * and can do what it is supposed to do.
+ */
+/*
+ *  Copyright The Mbed TLS Contributors
+ *  SPDX-License-Identifier: Apache-2.0
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License"); you may
+ *  not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+
+#ifndef PSA_EXERCISE_KEY_H
+#define PSA_EXERCISE_KEY_H
+
+#include "test/helpers.h"
+#include "test/psa_crypto_helpers.h"
+
+#include <psa/crypto.h>
+
+
+#endif /* PSA_EXERCISE_KEY_H */