reftable: order unittests by complexity

This is a more practical ordering when working on refactorings of the
reftable code.

Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/helper/test-reftable.c

@@ -3,15 +3,16 @@
 
 int cmd__reftable(int argc, const char **argv)
 {
+	/* test from simple to complex. */
 	basics_test_main(argc, argv);
+	record_test_main(argc, argv);
 	block_test_main(argc, argv);
-	merged_test_main(argc, argv);
+	tree_test_main(argc, argv);
 	pq_test_main(argc, argv);
-	record_test_main(argc, argv);
-	refname_test_main(argc, argv);
 	readwrite_test_main(argc, argv);
+	merged_test_main(argc, argv);
 	stack_test_main(argc, argv);
-	tree_test_main(argc, argv);
+	refname_test_main(argc, argv);
 	return 0;
 }