Merge #16551: test: Test that low difficulty chain fork is rejected

333317ce6b test: Test that low difficulty chain fork is rejected (MarcoFalke)
fa31dc1bf4 test: Pass down correct chain name in tests (MarcoFalke)

Pull request description:

  To prevent OOM, Bitcoin Core will reject chain forks at low difficulty by default. This is the only use-case of checkpoints, so add a test for it to make sure the feature works as expected. If it didn't work, checkpoints would have no use-case and we might as well remove them

ACKs for top commit:
  Sjors:
    Thanks for adding the node 1 example. Code review ACK 333317c

Tree-SHA512: 90dffa540d0904f3cffb61d2382b1a26f84fe9560b7013e4461546383add31a8757b350616a6d43217c59ef7b8b2a1b62bb3bab582c679cbb2c660a782ce7be1

test/functional/test_framework/util.py

@@ -287,14 +287,22 @@ def initialize_datadir(dirname, n, chain):
     datadir = get_datadir_path(dirname, n)
     if not os.path.isdir(datadir):
         os.makedirs(datadir)
+    # Translate chain name to config name
+    if chain == 'testnet3':
+        chain_name_conf_arg = 'testnet'
+        chain_name_conf_section = 'test'
+    else:
+        chain_name_conf_arg = chain
+        chain_name_conf_section = chain
     with open(os.path.join(datadir, "bitcoin.conf"), 'w', encoding='utf8') as f:
-        f.write("{}=1\n".format(chain))
-        f.write("[{}]\n".format(chain))
+        f.write("{}=1\n".format(chain_name_conf_arg))
+        f.write("[{}]\n".format(chain_name_conf_section))
         f.write("port=" + str(p2p_port(n)) + "\n")
         f.write("rpcport=" + str(rpc_port(n)) + "\n")
         f.write("server=1\n")
         f.write("keypool=1\n")
         f.write("discover=0\n")
+        f.write("dnsseed=0\n")
         f.write("listenonion=0\n")
         f.write("printtoconsole=0\n")
         f.write("upnp=0\n")