Add basic FillNewBlock test for empty mempool case

src/Makefile.gtest.include

@@ -9,6 +9,7 @@ zcash_gtest_SOURCES = \
 	gtest/test_checktransaction.cpp \
 	gtest/json_test_vectors.cpp \
         gtest/json_test_vectors.h \
+	gtest/test_fillnewblock.cpp \
 	gtest/test_foundersreward.cpp \
 	gtest/test_wallet_zkeys.cpp \
 	gtest/test_jsonspirit.cpp \

src/gtest/test_fillnewblock.cpp

@@ -0,0 +1,53 @@
+#include <gtest/gtest.h>
+
+#include "chain.h"
+#include "main.h"
+#include "miner.h"
+#include "primitives/block.h"
+#include "script/script.h"
+
+std::function<void(const uint256, double&, CAmount&)> noopApplyDeltas = []
+        (const uint256 hash, double &dPriorityDelta, CAmount &nFeeDelta) {
+    // No-op
+};
+
+TEST(FillNewBlock, EmptyMemPool) {
+    SelectParams(CBaseChainParams::MAIN);
+    const CChainParams& chainparams = Params();
+    CScript scriptDummy = CScript() << OP_TRUE;
+
+    auto prevHash = GetRandHash();
+    CBlockIndex indexPrev;
+    indexPrev.nHeight = 50;
+    indexPrev.phashBlock = &prevHash;
+
+    std::map<uint256, CTxMemPoolEntry> mapTx;
+
+    CBlock block;
+    std::vector<CAmount> vTxFees;
+    std::vector<int64_t> vTxSigOps;
+    FillNewBlock(&block, &indexPrev,
+                 scriptDummy, chainparams,
+                 vTxFees, vTxSigOps,
+                 mapTx, noopApplyDeltas,
+                 DEFAULT_BLOCK_MAX_SIZE,
+                 DEFAULT_BLOCK_PRIORITY_SIZE,
+                 DEFAULT_BLOCK_MIN_SIZE);
+
+    EXPECT_EQ(1, block.vtx.size());
+    EXPECT_EQ(1, vTxFees.size());
+    EXPECT_EQ(1, vTxSigOps.size());
+
+    const CTransaction& cb = block.vtx[0];
+    EXPECT_EQ(scriptDummy, cb.vout[0].scriptPubKey);
+    EXPECT_EQ(chainparams.GetFoundersRewardScriptAtHeight(51), cb.vout[1].scriptPubKey);
+
+    CAmount subsidy = GetBlockSubsidy(51, chainparams.GetConsensus());
+    CAmount fr = subsidy / 5;
+    subsidy -= fr;
+    EXPECT_EQ(subsidy, cb.vout[0].nValue);
+    EXPECT_EQ(fr, cb.vout[1].nValue);
+
+    EXPECT_EQ(0, vTxFees[0]);
+    EXPECT_EQ(0, vTxSigOps[0]);
+}