[test util] randomize fee in PopulateMempool

This makes the contents of the mempool more realistic and iterating by
ancestor feerate order more meaningful. If transactions have varying
feerates, it's also more likely that packages will need to be updated
during block template assembly.

Author: glozow

src/test/util/setup_common.cpp

@@ -397,15 +397,15 @@ std::vector<CTransactionRef> TestChain100Setup::PopulateMempool(FastRandomContex
             unspent_prevouts.pop_front();
         }
         const size_t num_outputs = det_rand.randrange(24) + 1;
-        // Approximately 1000sat "fee," equal output amounts.
-        const CAmount amount_per_output = (total_in - 1000) / num_outputs;
+        const CAmount fee = 100 * det_rand.randrange(30);
+        const CAmount amount_per_output = (total_in - fee) / num_outputs;
         for (size_t n{0}; n < num_outputs; ++n) {
             CScript spk = CScript() << CScriptNum(num_transactions + n);
             mtx.vout.push_back(CTxOut(amount_per_output, spk));
         }
         CTransactionRef ptx = MakeTransactionRef(mtx);
         mempool_transactions.push_back(ptx);
-        if (amount_per_output > 2000) {
+        if (amount_per_output > 3000) {
             // If the value is high enough to fund another transaction + fees, keep track of it so
             // it can be used to build a more complex transaction graph. Insert randomly into
             // unspent_prevouts for extra randomness in the resulting structures.
@@ -417,7 +417,9 @@ std::vector<CTransactionRef> TestChain100Setup::PopulateMempool(FastRandomContex
         if (submit) {
             LOCK2(m_node.mempool->cs, cs_main);
             LockPoints lp;
-            m_node.mempool->addUnchecked(CTxMemPoolEntry(ptx, 1000, 0, 1, false, 4, lp));
+            m_node.mempool->addUnchecked(CTxMemPoolEntry(ptx, /*fee=*/(total_in - num_outputs * amount_per_output),
+                                                         /*time=*/0, /*entry_height=*/1,
+                                                         /*spends_coinbase=*/false, /*sigops_cost=*/4, lp));
         }
         --num_transactions;
     }