[test] Add getblockchaininfo functional test #11370

Should assert values or types of each field?

value: only if you're testing a meaningful value type: I don't think we do this for other RPC methods, so I wouldn't bother

Thinking about this some more, perhaps we can add some utility method check_rpc_return_object(dict) which tests the presence and type of each field in the return object? Obviously not for this PR.

suggestion: perhaps add `self.log.info("test getblockchaininfo")

Done.

You can speed this test up by starting with pruning the first time, and then restart without pruning (saves one stop-start which is a slow operation). Do that by setting self.extra_args = [['-stopatheight=207', '-prune=1']] in set_test_params() and then setting self.extra_args = [['-stopatheight=207']] before restarting.

I think you can just use self.start_node(0). The default will use self.extra_args[0] for its args.

Convenient method to stop and start a node with the same arguments as before. If this gets ACK's I can push a commit to use where appropriate or submit this in a separate PR.

Great! Ideally the stop and start methods in TestFramework would be methods on the TestNode class, and so would this, but we can clean that up later.

You can change this to:

def restart_node(self, i):
    """Stop and start a test node"""
    self.stop_node(i)
    self.start_node(i)

As long as you also take my change to blockchain.py above.

Sorry, I misled you here. You should use self.nodes[0].extra_args = .... The self.extra_args class variable is only used when instantiating the TestNode. That's important for restart_node()

@jnewbery added the option to override node.extra_args. I wonder if that this new extra_arg should be saved in node.

Looks good. I don't think you need to update node.extra_args