test: add block 2016 to mock mainnet

The next commit requires an additional mainnet block which changes the difficulty.

Also fix a few minor mistakes in the test (suite):
- rename the create_coinbase retarger_period argument to halving_period. Before bitcoin#31583 this was hardcoded for regtest where these values are the same.
- drop unused fees argument from mine helper

Finally the CPU miner instructions for generating the alternative mainnet chain are expanded.

Github-Pull: #33446
Rebased-From: 4c3c1f42cf

test/functional/mining_mainnet.py

@@ -53,15 +53,15 @@ class MiningMainnetTest(BitcoinTestFramework):
             help='Block data file (default: %(default)s)',
         )
 
-    def mine(self, height, prev_hash, blocks, node, fees=0):
+    def mine(self, height, prev_hash, blocks, node):
         self.log.debug(f"height={height}")
         block = CBlock()
         block.nVersion = 0x20000000
         block.hashPrevBlock = int(prev_hash, 16)
         block.nTime = blocks['timestamps'][height - 1]
-        block.nBits = DIFF_1_N_BITS
+        block.nBits = DIFF_1_N_BITS if height < 2016 else DIFF_4_N_BITS
         block.nNonce = blocks['nonces'][height - 1]
-        block.vtx = [create_coinbase(height=height, script_pubkey=bytes.fromhex(COINBASE_SCRIPT_PUBKEY), retarget_period=2016)]
+        block.vtx = [create_coinbase(height=height, script_pubkey=bytes.fromhex(COINBASE_SCRIPT_PUBKEY), halving_period=210000)]
         # The alternate mainnet chain was mined with non-timelocked coinbase txs.
         block.vtx[0].nLockTime = 0
         block.vtx[0].vin[0].nSequence = SEQUENCE_FINAL
@@ -82,12 +82,15 @@ class MiningMainnetTest(BitcoinTestFramework):
         self.log.info("Load alternative mainnet blocks")
         path = os.path.join(os.path.dirname(os.path.realpath(__file__)), self.options.datafile)
         prev_hash = node.getbestblockhash()
+        blocks = None
         with open(path, encoding='utf-8') as f:
             blocks = json.load(f)
             n_blocks = len(blocks['timestamps'])
-            assert_equal(n_blocks, 2015)
-            for i in range(2015):
-                prev_hash = self.mine(i + 1, prev_hash, blocks, node)
+            assert_equal(n_blocks, 2016)
+
+        # Mine up to the last block of the first retarget period
+        for i in range(2015):
+            prev_hash = self.mine(i + 1, prev_hash, blocks, node)
 
         assert_equal(node.getblockcount(), 2015)
 
@@ -102,5 +105,9 @@ class MiningMainnetTest(BitcoinTestFramework):
         assert_equal(mining_info['next']['bits'], nbits_str(DIFF_4_N_BITS))
         assert_equal(mining_info['next']['target'], target_str(DIFF_4_TARGET))
 
+        # Mine first block of the second retarget period
+        height = 2016
+        prev_hash = self.mine(height, prev_hash, blocks, node)
+        assert_equal(node.getblockcount(), height)
 if __name__ == '__main__':
     MiningMainnetTest(__file__).main()