Ensure mutex test mutex gets free'd

Signed-off-by: Paul Elliott <paul.elliott@arm.com>
diff --git a/tests/src/threading_helpers.c b/tests/src/threading_helpers.c
index 385a079..434d124 100644
--- a/tests/src/threading_helpers.c
+++ b/tests/src/threading_helpers.c
@@ -228,4 +228,14 @@
     mbedtls_test_info.mutex_usage_error = NULL;
 }
 
+void mbedtls_test_mutex_usage_end(void)
+{
+    mbedtls_mutex_init = mutex_functions.init;
+    mbedtls_mutex_free = mutex_functions.free;
+    mbedtls_mutex_lock = mutex_functions.lock;
+    mbedtls_mutex_unlock = mutex_functions.unlock;
+
+    mutex_functions.free(&mbedtls_test_mutex_mutex);
+}
+
 #endif /* MBEDTLS_TEST_MUTEX_USAGE */