test: io: add test case for hostname == NULL

Signed-off-by: Tadeusz Struk <tadeusz.struk@intel.com>
diff --git a/test/unit/io.c b/test/unit/io.c
index aee7e6e..f0226aa 100644
--- a/test/unit/io.c
+++ b/test/unit/io.c
@@ -119,6 +119,17 @@
     rc = socket_connect ("127.0.0.1", 444, &sock);
     assert_int_equal (rc, TSS2_TCTI_RC_IO_ERROR);
 }
+
+static void
+socket_connect_null_test (void **state)
+{
+    TSS2_RC rc;
+    SOCKET sock;
+
+    rc = socket_connect (NULL, 444, &sock);
+    assert_int_equal (rc, TSS2_TCTI_RC_BAD_REFERENCE);
+}
+
 int
 main (int   argc,
       char *argv[])
@@ -126,6 +137,7 @@
     const struct CMUnitTest tests[] = {
         cmocka_unit_test (write_all_simple_success_test),
         cmocka_unit_test (socket_connect_test),
+        cmocka_unit_test (socket_connect_null_test),
         cmocka_unit_test (socket_connect_socket_fail_test),
         cmocka_unit_test (socket_connect_connect_fail_test),
     };