Does code return an object inheriting from the expected base type, S3 class, or S4 class?

See https://adv-r.hadley.nz/oo.html for an overview of R's OO systems, and the vocabulary used here.

• expect_type(x, type) checks that typeof(x) is type.

• expect_s3_class(x, class) checks that x is an S3 object that inherits() from class

• expect_s4_class(x, class) checks that x is an S4 object that is() class.

See expect_vector() for testing properties of objects created by vctrs.

expect_type(object, type)

expect_s3_class(object, class, exact = FALSE)

expect_s4_class(object, class)

Arguments

object	Object to test. Supports limited unquoting to make it easier to generate readable failures within a function or for loop. See quasi_label for more details.
type	String giving base type (as returned by typeof()).
class	character vector of class names
exact	If FALSE, the default, checks that object inherits from class. If TRUE, checks that object has a class that's identical to class.

See also

Other expectations: comparison-expectations, equality-expectations, expect_error(), expect_length(), expect_match(), expect_named(), expect_null(), expect_output(), expect_reference(), expect_silent(), logical-expectations

Examples

x <- data.frame(x = 1:10, y = "x", stringsAsFactors = TRUE)
# A data frame is an S3 object with class data.frame
expect_s3_class(x, "data.frame")
show_failure(expect_s4_class(x, "data.frame"))
#> Failed expectation:
#> `x` is not an S4 object
# A data frame is built from a list:
expect_type(x, "list")

# An integer vector is an atomic vector of type "integer"
expect_type(x$x, "integer")
# It is not an S3 object
show_failure(expect_s3_class(x$x, "integer"))
#> Failed expectation:
#> x$x is not an S3 object

# Above, we requested data.frame() converts strings to factors:
show_failure(expect_type(x$y, "character"))
#> Failed expectation:
#> x$y has type `integer`, not `character`.
expect_s3_class(x$y, "factor")
expect_type(x$y, "integer")