expect_s3_class for class hierarchies

[krlmlr]

What's a good way to test that an object inherits from multiple classes? expect_s3_class() uses inherits() which tests if the object inherits from one of the classes passed.

Can we add a new expect_s3_classes() ?

# This is expected
testthat::expect_s3_classes(tibble::tibble(), c("tbl_df", "data.frame"))
# This should be a failure?
testthat::expect_s3_classes(tibble::tibble(), c("tbl_df", "data.table"))

^{Created on 2019-06-15 by the reprex package (v0.3.0)}

[jimhester]

You can use inherits(which = TRUE) to test all classes, it returns the indexes of the matches, or 0 if there are no matches.

all(inherits(tibble::tibble(), c("tbl_df", "data.frame"), which = TRUE) > 0)
#> [1] TRUE
all(inherits(tibble::tibble(), c("tbl_df", "data.table"), which = TRUE) > 0)
#> [1] FALSE

^{Created on 2019-06-17 by the reprex package (v0.3.0)}

[krlmlr]

Is it worthwhile to turn this pattern into a first-class expectation?

[jimhester]

It might be worth seeing how many packages break if we just make this behavior the default for expect_s3_class(), it seems to me like testing for all the classes is a more useful default than testing for any of them, like it is currently.

[lionel-]

You can also use rlang::inherits_all() and rlang::inherits_only() in combination with expect_true().

[Eluvias]

Similar to #667

[hadley]

Maybe we could add an exact = TRUE argument?

[ha0ye]

Adding a +1 that I think exact = TRUE should be a default, as I otherwise missed a typo in checking against a vector of classes.