R CMD检查 - 包可以安装但不能加载

我创建了一个名为 letstrythis 的测试包来说明问题 . 测试包非常简单，包含以下文件：

• DESCRIPTION

Package: letstrythis
Title: What the Package Does (one line, title case)
Version: 0.0.0.9000
Authors@R: person("Mike", "Smith", email = "Mike.Smith@anything.com", role = c("aut", "cre"))
Description: letstrythis is great.
Depends:
    R (>= 3.2.3)
License: GPL
LazyData: true
Maintainer: 'Mike Smith' <Mike.Smith@anything.com>
RoxygenNote: 5.0.1

• NAMESPACE

# Generated by roxygen2: do not edit by hand
export(add_numbers)

• R/add-numbers.R

#' test function
#'
#' @param x numeric
#' @param y numeric
#' @return numeric
#' @export
#'
#' @examples
#' add_numbers(1, 1)
#' add_numbers(2, 3)


add_numbers <- function(x, y) {
  x + y
}

和

• man/add_numbers.Rd

这是由roxygen2自动创建的 .

每次我用 devtools::check() 检查我的包时，都会收到以下错误消息：

* checking examples ... ERROR
Running examples in 'letstrythis-Ex.R' failed
The error occurred in:

R version 3.2.3 (2015-12-10) -- "Wooden Christmas-Tree"
Copyright (C) 2015 The R Foundation for Statistical Computing
Platform: x86_64-w64-mingw32/x64 (64-bit)

R is free software and comes with ABSOLUTELY NO WARRANTY.
You are welcome to redistribute it under certain conditions.
Type 'license()' or 'licence()' for distribution details.

  Natural language support but running in an English locale

R is a collaborative project with many contributors.
Type 'contributors()' for more information and
'citation()' on how to cite R or R packages in publications.

Type 'demo()' for some demos, 'help()' for on-line help, or
'help.start()' for an HTML browser interface to help.
Type 'q()' to quit R.

> pkgname <- "letstrythis"
> source(file.path(R.home("share"), "R", "examples-header.R"))
> options(warn = 1)
> options(pager = "console")
> base::assign(".ExTimings", "letstrythis-Ex.timings", pos = 'CheckExEnv')
> base::cat("name\tuser\tsystem\telapsed\n", file=base::get(".ExTimings", pos = 'CheckExEnv'))
> base::assign(".format_ptime",
+ function(x) {
+   if(!is.na(x[4L])) x[1L] <- x[1L] + x[4L]
+   if(!is.na(x[5L])) x[2L] <- x[2L] + x[5L]
+   options(OutDec = '.')
+   format(x[1L:3L], digits = 7L)
+ },
+ pos = 'CheckExEnv')
> 
> ### * </HEADER>
> library('letstrythis')
Error in library("letstrythis") : 
  there is no package called 'letstrythis'
Execution halted
* checking PDF version of manual ... OK
* DONE
Status: 1 ERROR

See
  'Z:/R_codes/letstrythis.Rcheck/00check.log'
for details.

Error: Command failed (1)
Execution halted

Exited with status 1.

每次执行 R/add-numbers.R 中的示例时，无法使用 library() 加载包 .