message: tests: add utility to assert node memory usage hasn't increased
  Adds a utility to get resident set size memory usage for a test
  node and a context manager that allows assertions based upon
  maximum memory use increase.
diff: @@ -115,6 +115,28 @@ class TestNode():
  ]
  return PRIV_KEYS[self.index]
  + def get_mem_rss(self):
  + """Get the memory usage (RSS) per `ps`.
  +
  + If process is stopped or `ps` is unavailable, return None.
  + """
  + if not (self.running and self.process):
  + self.log.warning("Couldn't get memory usage; process isn't running.")
  + return None
  +
  + try:
  + return int(subprocess.check_output(
  + "ps h -o rss {}".format(self.process.pid),
  + shell=True, stderr=subprocess.DEVNULL).strip())
  +
  + # Catching `Exception` broadly to avoid failing on platforms where ps
  + # isn't installed or doesn't work as expected, e.g. OpenBSD.
  + #
  + # We could later use something like `psutils` to work across platforms.
  + except Exception:
  + self.log.exception("Unable to get memory usage")
  + return None
  +
  def _node_msg(self, msg: str) -> str:
  """Return a modified msg that identifies this node by its index as a debugging aid."""
  return "[node %d] %s" % (self.index, msg)
  @@ -267,6 +289,29 @@ class TestNode():
  if re.search(re.escape(expected_msg), log, flags=re.MULTILINE) is None:
  self._raise_assertion_error('Expected message "{}" does not partially match log:\n\n{}\n\n'.format(expected_msg, print_log))
  + @contextlib.contextmanager
  + def assert_memory_usage_stable(self, perc_increase_allowed=0.03):
  + """Context manager that allows the user to assert that a node's memory usage (RSS)
  + hasn't increased beyond some threshold percentage.
  + """
  + before_memory_usage = self.get_mem_rss()
  +
  + yield
  +
  + after_memory_usage = self.get_mem_rss()
  +
  + if not (before_memory_usage and after_memory_usage):
  + self.log.warning("Unable to detect memory usage (RSS) - skipping memory check.")
  + return
  +
  + perc_increase_memory_usage = 1 - (float(before_memory_usage) / after_memory_usage)
  +
  + if perc_increase_memory_usage > perc_increase_allowed:
  + self._raise_assertion_error(
  + "Memory usage increased over threshold of {:.3f}% from {} to {} ({:.3f}%)".format(
  + perc_increase_allowed * 100, before_memory_usage, after_memory_usage,
  + perc_increase_memory_usage * 100))
  +
  def assert_start_raises_init_error(self, extra_args=None, expected_msg=None, match=ErrorMatch.FULL_TEXT, *args, **kwargs):
  """Attempt to start the node and expect it to raise an error.
  