testing-r-packages

# Testing R Packages with testthat Modern best practices for R package testing using testthat 3+. ## Initial Setup Initialize testing with testthat 3rd edition: ```r usethis::use_testthat(3) ``` This creates `tests/testthat/` directory, adds testthat to `DESCRIPTION` Suggests with `Config/testthat/edition: 3`, and creates `tests/testthat.R`. ## File Organization **Mirror package structure:** - Code in `R/foofy.R` → tests in `tests/testthat/test-foofy.R` - Use `usethis::use_r("foofy")` and `usethis::use_test("foofy")` to create paired files **Special files:** - `helper-*.R` - Helper functions and custom expectations, sourced before tests - `setup-*.R` - Run during `R CMD check` only, not during `load_all()` - `fixtures/` - Static test data files accessed via `test_path()` ## Test Structure Tests follow a three-level hierarchy: **File → Test → Expectation** ### Standard Syntax ```r test_that("descriptive behavior", { result <- my_function(input) expect_equal(result, expected_value) }) ``` **Test descriptions** should read naturally and describe behavior, not implementation. ### BDD Syntax (describe/it) For behavior-driven development, use `describe()` and `it()`: ```r describe("matrix()", { it("can be multiplied by a scalar", { m1 <- matrix(1:4, 2, 2) m2 <- m1 * 2 expect_equal(matrix(1:4 * 2, 2, 2), m2) }) it("can be transposed", { m <- matrix(1:4, 2, 2) expect_equal(t(m), matrix(c(1, 3, 2, 4), 2, 2)) }) }) ``` **Key features:**...