code: func ExpectConnectionProblem(c *check.C, err error) {
  	c.Assert(trace.IsConnectionProblem(err), check.Equals, true, check.Commentf("expected ConnectionProblem, got %T %v at %v", trace.Unwrap(err), err, string(debug.Stack())))
  }
docs: // ExpectConnectionProblem expects connection problem error