Merge #7705: [amount] Add tests and make GetFee() monotonic

fad13b1 [amount] Preempt issues with negative fee rates (MarcoFalke)
faf756a [amount] Make GetFee() monotonic (MarcoFalke)
fab6880 [qa] Add amount tests (MarcoFalke)

4 files changed, 54 insertions, 7 deletions

diff --git a/src/Makefile.test.include b/src/Makefile.test.include
index 57f9ac50e0..820a144a95 100644
--- a/src/Makefile.test.include
+++ b/src/Makefile.test.include
@@ -38,6 +38,7 @@ BITCOIN_TESTS =\
   test/scriptnum10.h \
   test/addrman_tests.cpp \
   test/alert_tests.cpp \
+  test/amount_tests.cpp \
   test/allocator_tests.cpp \
   test/base32_tests.cpp \
   test/base58_tests.cpp \
diff --git a/src/amount.cpp b/src/amount.cpp
index a3abd8cd83..68806ff062 100644
--- a/src/amount.cpp
+++ b/src/amount.cpp
@@ -19,10 +19,10 @@ CFeeRate::CFeeRate(const CAmount& nFeePaid, size_t nSize)
 
 CAmount CFeeRate::GetFee(size_t nSize) const
 {
-    CAmount nFee = nSatoshisPerK*nSize / 1000;
+    CAmount nFee = nSatoshisPerK * nSize / 1000;
 
-    if (nFee == 0 && nSatoshisPerK > 0)
-        nFee = nSatoshisPerK;
+    if (nFee == 0 && nSize != 0 && nSatoshisPerK > 0)
+        nFee = CAmount(1);
 
     return nFee;
 }
diff --git a/src/amount.h b/src/amount.h
index a48b17d514..9aba6525c7 100644
--- a/src/amount.h
+++ b/src/amount.h
@@ -42,10 +42,14 @@ public:
     explicit CFeeRate(const CAmount& _nSatoshisPerK): nSatoshisPerK(_nSatoshisPerK) { }
     CFeeRate(const CAmount& nFeePaid, size_t nSize);
     CFeeRate(const CFeeRate& other) { nSatoshisPerK = other.nSatoshisPerK; }
-
-    CAmount GetFee(size_t size) const; // unit returned is satoshis
-    CAmount GetFeePerK() const { return GetFee(1000); } // satoshis-per-1000-bytes
-
+    /**
+     * Return the fee in satoshis for the given size in bytes.
+     */
+    CAmount GetFee(size_t size) const;
+    /**
+     * Return the fee in satoshis for a size of 1000 bytes
+     */
+    CAmount GetFeePerK() const { return GetFee(1000); }
     friend bool operator<(const CFeeRate& a, const CFeeRate& b) { return a.nSatoshisPerK < b.nSatoshisPerK; }
     friend bool operator>(const CFeeRate& a, const CFeeRate& b) { return a.nSatoshisPerK > b.nSatoshisPerK; }
     friend bool operator==(const CFeeRate& a, const CFeeRate& b) { return a.nSatoshisPerK == b.nSatoshisPerK; }
diff --git a/src/test/amount_tests.cpp b/src/test/amount_tests.cpp
new file mode 100644
index 0000000000..59dab20633
--- /dev/null
+++ b/src/test/amount_tests.cpp
@@ -0,0 +1,42 @@
+// Copyright (c) 2016 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 "test/test_bitcoin.h"
+
+#include <boost/test/unit_test.hpp>
+
+BOOST_FIXTURE_TEST_SUITE(amount_tests, BasicTestingSetup)
+
+BOOST_AUTO_TEST_CASE(GetFeeTest)
+{
+    CFeeRate feeRate;
+
+    feeRate = CFeeRate(0);
+    // Must always return 0
+    BOOST_CHECK_EQUAL(feeRate.GetFee(0), 0);
+    BOOST_CHECK_EQUAL(feeRate.GetFee(1e5), 0);
+
+    feeRate = CFeeRate(1000);
+    // Must always just return the arg
+    BOOST_CHECK_EQUAL(feeRate.GetFee(0), 0);
+    BOOST_CHECK_EQUAL(feeRate.GetFee(1), 1);
+    BOOST_CHECK_EQUAL(feeRate.GetFee(121), 121);
+    BOOST_CHECK_EQUAL(feeRate.GetFee(999), 999);
+    BOOST_CHECK_EQUAL(feeRate.GetFee(1e3), 1e3);
+    BOOST_CHECK_EQUAL(feeRate.GetFee(9e3), 9e3);
+
+    feeRate = CFeeRate(123);
+    // Truncates the result, if not integer
+    BOOST_CHECK_EQUAL(feeRate.GetFee(0), 0);
+    BOOST_CHECK_EQUAL(feeRate.GetFee(8), 1); // Special case: returns 1 instead of 0
+    BOOST_CHECK_EQUAL(feeRate.GetFee(9), 1);
+    BOOST_CHECK_EQUAL(feeRate.GetFee(121), 14);
+    BOOST_CHECK_EQUAL(feeRate.GetFee(122), 15);
+    BOOST_CHECK_EQUAL(feeRate.GetFee(999), 122);
+    BOOST_CHECK_EQUAL(feeRate.GetFee(1e3), 123);
+    BOOST_CHECK_EQUAL(feeRate.GetFee(9e3), 1107);
+}
+
+BOOST_AUTO_TEST_SUITE_END()