docstring not working on functions starting with dot(.)

[Jiayou-Chao]

.test <- function(x) {
  #' A test function
  #' @param x a number
  return(x+1)
}

test <- function(x) {
  #' A test function
  #' @param x a number
  return(x+1)
}

docstring(test) works but docstring(.test) throws an error:

The specified rdFile 'AppData\Local\Temp\RtmpUPOF2L/TempPackage/man/.test.Rd' does not exist.