Merge bitcoin/bitcoin#35193: test: avoid non-loopback network traffic from node_init_tests/init_test

1c500b1709 test: avoid non-loopback network traffic from node_init_tests/init_test (Vasil Dimov)

Pull request description:

  The test `node_init_tests/init_test` calls:
  `AppInitMain()` -> `StartMapPort()` -> `StartThreadMapPort()` -> `ThreadMapPort()` -> `ProcessPCP()` -> `PCPRequestPortMap()` -> `CreateSock()` and on the returned value from `CreateSock()` it calls the `Connect()` method.

  Thus, change `BasicTestingSetup::BasicTestingSetup()` to set `-natpmp` to 0. This way `node_init_tests/init_test` or other tests will not do network activity due to `ThreadMapPort()`.

  Also add a comment about `natpmp=0` in
  `test/functional/test_framework/util.py`.

  Also set `-dnsseed=0` in `BasicTestingSetup::BasicTestingSetup()` to
  avoid DNS queries.

ACKs for top commit:
  fjahr:
    re-ACK 1c500b1709
  ryanofsky:
    Code review ACK 1c500b1709, just disabling -dnsseed since previous review, which makes sense.

Tree-SHA512: 3b275d91361804da6d1dc109dffe741ea4b3dd3be916eb12fa63efa233e13ea4dab5a9f8448bd8bf99bc41817f3b7a768abe91531a3f63eae8b4c912bfcbd13e

src/test/util/setup_common.cpp

@@ -199,6 +199,10 @@ BasicTestingSetup::BasicTestingSetup(const ChainType chainType, TestOpts opts)
     m_args.ForceSetArg("-datadir", fs::PathToString(m_path_root));
     gArgs.ForceSetArg("-datadir", fs::PathToString(m_path_root));
 
+    // Avoid non-loopback network traffic during tests.
+    gArgs.ForceSetArg("-dnsseed", "0"); // DNS queries are usually forwarded to upstream DNS servers.
+    gArgs.ForceSetArg("-natpmp", "0"); // NATPMP sends packets to the router.
+
     SelectParams(chainType);
     InitLogging(*m_node.args);
     AppInitParameterInteraction(*m_node.args);

test/functional/test_framework/util.py

@@ -576,7 +576,7 @@ def write_config(config_path, *, n, chain, extra_config="", disable_autoconnect=
         # in tests.
         f.write("peertimeout=999999999\n")
         f.write("printtoconsole=0\n")
-        f.write("natpmp=0\n")
+        f.write("natpmp=0\n") # Avoid non-loopback network traffic during tests.
         f.write("shrinkdebugfile=0\n")
         # To improve SQLite wallet performance so that the tests don't timeout, use -unsafesqlitesync
         f.write("unsafesqlitesync=1\n")