test: Add FeeFilterRounder test

src/Makefile.test.include

@@ -231,6 +231,7 @@ BITCOIN_TESTS =\
   test/net_tests.cpp \
   test/netbase_tests.cpp \
   test/pmt_tests.cpp \
+  test/policy_fee_tests.cpp \
   test/policyestimator_tests.cpp \
   test/pow_tests.cpp \
   test/prevector_tests.cpp \

src/test/policy_fee_tests.cpp

@@ -0,0 +1,34 @@
+// Copyright (c) 2020 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <amount.h>
+#include <policy/fees.h>
+
+#include <test/util/setup_common.h>
+
+#include <boost/test/unit_test.hpp>
+
+BOOST_FIXTURE_TEST_SUITE(policy_fee_tests, BasicTestingSetup)
+
+BOOST_AUTO_TEST_CASE(FeeRounder)
+{
+    FeeFilterRounder fee_rounder{CFeeRate{1000}};
+
+    // check that 1000 rounds to 974 or 1071
+    std::set<CAmount> results;
+    while (results.size() < 2) {
+        results.emplace(fee_rounder.round(1000));
+    }
+    BOOST_CHECK_EQUAL(*results.begin(), 974);
+    BOOST_CHECK_EQUAL(*++results.begin(), 1071);
+
+    // check that negative amounts rounds to 0
+    BOOST_CHECK_EQUAL(fee_rounder.round(-0), 0);
+    BOOST_CHECK_EQUAL(fee_rounder.round(-1), 0);
+
+    // check that MAX_MONEY rounds to 9170997
+    BOOST_CHECK_EQUAL(fee_rounder.round(MAX_MONEY), 9170997);
+}
+
+BOOST_AUTO_TEST_SUITE_END()