R package fails devtools::check, because “could not find function” even though the function is imported in NAMESPACE

问题

Trying to build my first R package using roxygen2 and devtools. I have added a function that uses %>% and mutate in the @examples section. When I run check() it fails, because it cannot find the function %>% or mutate.

Based on this, this, and this I have tried the following:

I have #' importFrom magrittr %>% and #' importFrom dplyr mutate in the function's .R file. I also have magrittr and dplyr under Imports: in the DESCRIPTION file. After running document(), my NAMESPACE file contains importFrom(dplyr,mutate) and importFrom(magrittr,"%>%").

minimal R/test.R file:

#' Conditional mutate
#'
#' \code{mutate_cond} mutates the \code{data.frame} only on the rows that
#' satisfy the condition.
#' 
#' @param .data \code{data.frame}
#' @param condition expression with the condition to be evaluated
#' @param ... arguments passed to \code{mutate}
#' @param envir environment inherited from \code{parent.frame()}
#'
#' @return \code{data.frame}
#' @importFrom dplyr mutate
#' @importFrom magrittr %>%
#'
#' @examples
#' data(iris)
#' iris %>%
#'    mutate(aux = 0) %>%
#'    mutate_cond(Petal.Length > 1.3,aux = 3)
#'
#' @export
mutate_cond <- function(.data, condition, ..., envir = parent.frame()) {
  condition <- eval(substitute(condition), .data, envir)
  .data[condition, ] <- .data[condition, ] %>% mutate(...)
  .data
}

minimal DESCRIPTION file:

Package: test
Version: 0.1
Date: 2019-06-07
Title: Functions
Description: Some functions I use.
Author: me
Maintainer: me <myemail@email.com>
Encoding: UTF-8
License: GPL-3
Imports: dplyr, magrittr

NAMESPACE generated with document():

# Generated by roxygen2: do not edit by hand

export(mutate_cond)
importFrom(dplyr,mutate)
importFrom(magrittr,"%>%")

I expect this example code to run successfully and pass check(). Instead I get this error message:

❯ checking examples ... ERROR
  Running examples in ‘test-Ex.R’ failed
  The error most likely occurred in:

  > base::assign(".ptime", proc.time(), pos = "CheckExEnv")
  > ### Name: mutate_cond
  > ### Title: Conditional mutate
  > ### Aliases: mutate_cond
  > 
  > ### ** Examples
  > 
  > data(iris)
  > iris %>%
  +    mutate(aux = 0) %>%
  +    mutate_cond(Petal.Length > 1.3,aux = 3)
  Error in iris %>% mutate(aux = 0) %>% mutate_cond(Petal.Length > 1.3,  : 
    could not find function "%>%"
  Execution halted

1 error ✖ | 0 warnings ✔ | 0 notes ✔

Also, if I add require(dplyr) and require(magrittr) to the @examples section the error goes away or if I remove the whole @examples section the error goes away.

Why won't this package pass check()?

Thank you!