# Workflow: Projects, Version Control, Testing and Packages — R Programming

Source: https://www.geekswithgeeks.com/en/r-programming/p-workflow

> Organise R work professionally with projects, Git, tests and packages.

## Professional R habits

Analysis code deserves the same care as software. Use **projects** with a consistent layout (`data/raw`, `data/processed`, `R/` for functions, `analysis/` or `reports/`, `output/`), relative paths (the **here** package's `here::here("data", "raw.csv")` helps), and **never modify raw data** by hand: clean it in code. Put the project under **Git** version control (RStudio and Positron integrate it) and lock package versions with **renv**. Move repeated code into **functions** in `R/` files. Test functions with **testthat** (`test_that("...", { expect_equal(...) })`). When functions are reused across projects, turn them into an **R package**: **usethis** creates the structure (`usethis::create_package()`), **roxygen2** generates documentation from comments, **devtools** builds, loads and checks it (`devtools::check()`), and packages can be shared internally or on CRAN. Style code consistently with the **tidyverse style guide**, automated by **styler** and checked by **lintr**. For pipelines with many steps, the **targets** package rebuilds only outdated steps, like a Makefile for analyses.

## Tests for an analysis function and package scaffolding

testthat checks behaviour; usethis and devtools manage packages.

```r
# R/gst.R
gst_total <- function(amount, rate = 0.18) {
  stopifnot(is.numeric(amount), rate >= 0)
  round(amount * (1 + rate), 2)
}

# tests/testthat/test-gst.R
library(testthat)

test_that("gst_total adds the default 18% GST", {
  expect_equal(gst_total(100), 118)
  expect_equal(gst_total(c(100, 200)), c(118, 236))
})

test_that("gst_total rejects non-numeric input", {
  expect_error(gst_total("100"))
})

# turning reusable code into a package
# usethis::create_package("~/code/salestools")
# usethis::use_r("gst")
# usethis::use_testthat()
# devtools::document()   # roxygen2 comments -> help pages
# devtools::test()
# devtools::check()      # full package checks, as CRAN runs them
```

## Raw data is read-only

Keep raw files untouched and write every cleaning step in code. If someone asks how a number was produced, you can show the exact path from source to result.

**Quiz:** Which package is commonly used for writing unit tests in R?

- [x] testthat
- [ ] ggplot2
- [ ] lubridate
- [ ] shiny

*Answer:* testthat. testthat provides expect_* functions and is the standard for R tests.