unit-tests: Add mock nonce generator

We don't make the full nonces configurable but only the first byte,
which should be enough to force a nonce to be smaller than others.

src/libcharon/tests/utils/mock_nonce_gen.h

@@ -0,0 +1,37 @@
+/*
+ * Copyright (C) 2016 Tobias Brunner
+ * HSR Hochschule fuer Technik Rapperswil
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation; either version 2 of the License, or (at your
+ * option) any later version.  See <http://www.fsf.org/copyleft/gpl.txt>.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * for more details.
+ */
+
+/**
+ * Special nonce generator that sets the first byte of the generated nonces to
+ * a fixed specified value.
+ *
+ * @defgroup mock_nonce_gen mock_nonce_gen
+ * @{ @ingroup test_utils_c
+ */
+
+#ifndef MOCK_NONCE_GEN_H_
+#define MOCK_NONCE_GEN_H_
+
+#include <crypto/nonce_gen.h>
+
+/**
+ * Creates a nonce_gen_t instance.
+ *
+ * @param first		first byte to set in generated nonces
+ * @return			created object
+ */
+nonce_gen_t *mock_nonce_gen_create(u_char first);
+
+#endif /** MOCK_NONCE_GEN_H_ @} */