Require usage of expect_s4_class(x, k) over expect_true(is(x, k))
Source:R/expect_s3_class_linter.R
expect_s4_class_linter.Rdtestthat::expect_s4_class() exists specifically for testing the class
of S4 objects. 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.