Require usage of expect_null for checking NULL

Require usage of expect_null(x) over expect_equal(x, NULL) and similar usages.

Usage

expect_null_linter()

Details

testthat::expect_null() exists specifically for testing for NULL objects. testthat::expect_equal(), testthat::expect_identical(), and testthat::expect_true() can also be used for such tests, but it is better to use the tailored function instead.

See also

linters for a complete list of linters available in lintr.

Tags

best_practices, package_development, pkg_testthat

Examples

# will produce lints
lint(
  text = "expect_equal(x, NULL)",
  linters = expect_null_linter()
)
#> <text>:1:1: warning: [expect_null_linter] expect_null(x) is better than expect_equal(x, NULL)
#> expect_equal(x, NULL)
#> ^~~~~~~~~~~~~~~~~~~~~

lint(
  text = "expect_identical(x, NULL)",
  linters = expect_null_linter()
)
#> <text>:1:1: warning: [expect_null_linter] expect_null(x) is better than expect_identical(x, NULL)
#> expect_identical(x, NULL)
#> ^~~~~~~~~~~~~~~~~~~~~~~~~

lint(
  text = "expect_true(is.null(x))",
  linters = expect_null_linter()
)
#> <text>:1:1: warning: [expect_null_linter] expect_null(x) is better than expect_true(is.null(x))
#> expect_true(is.null(x))
#> ^~~~~~~~~~~~~~~~~~~~~~~


# okay
lint(
  text = "expect_null(x)",
  linters = expect_null_linter()
)
#> ℹ No lints found.