tests: add bn_write_be

tests.c

@@ -100,6 +100,17 @@ START_TEST(test_bignum_read_be)
 }
 END_TEST
 
+START_TEST(test_bignum_write_be)
+{
+	bignum256 a = { { 0x286d8bd5, 0x380c7c17, 0x3c6a2ec1, 0x2d787ef5, 0x14437cd3, 0x25a043f8, 0x1dd5263f, 0x33a162c3, 0x0000c55e } };
+	uint8_t tmp[32];
+
+	bn_write_be(&a, tmp);
+
+	ck_assert_mem_eq(tmp, fromhex("c55ece858b0ddd5263f96810fe14437cd3b5e1fbd7c6a2ec1e031f05e86d8bd5"), 32);
+}
+END_TEST
+
 
 // from https://github.com/bitcoin/bitcoin/blob/master/src/test/data/base58_keys_valid.json
 START_TEST(test_base58)
@@ -2347,6 +2358,7 @@ Suite *test_suite(void)
 
 	tc = tcase_create("bignum");
 	tcase_add_test(tc, test_bignum_read_be);
+	tcase_add_test(tc, test_bignum_write_be);
 	suite_add_tcase(s, tc);
 
 	tc = tcase_create("base58");