include private pk.h internally

Signed-off-by: Ben Taylor <ben.taylor@linaro.org>
diff --git a/tests/suites/test_suite_debug.function b/tests/suites/test_suite_debug.function
index 57b8f4e..1d37137 100644
--- a/tests/suites/test_suite_debug.function
+++ b/tests/suites/test_suite_debug.function
@@ -2,6 +2,9 @@
 #include "debug_internal.h"
 #include "string.h"
 #include "mbedtls/pk.h"
+#if defined(MBEDTLS_PK_HAVE_PRIVATE_HEADER)
+#include <mbedtls/private/pk_private.h>
+#endif /* MBEDTLS_PK_HAVE_PRIVATE_HEADER */
 #include <test/ssl_helpers.h>
 
 #if defined(_WIN32)