expect_s3_class Test Unexpectedly Still Holds True

[DarioS]

Using ggplot2 4.0.0, a check for S3 class still passes. Isn't it S7 nowadays?

library(ggplot2)
p <- ggplot(mtcars, aes(wt, mpg))
show_failure(expect_s3_class(p, "ggplot")) # Nothing.

Breaking Changes
The S3 parts of ggplot2 have been replaced with S7 bits.

[teunbrand]

Yes, that's right: it is S7 these days. Technically S7 objects are S3 objects, because S7 is implemented on top of S3. For backward compatibility, we append the S3 class to not break that specific expectation. Ideally, unit testing should be done using expect_true(is_ggplot(<object>)) which will be consistent with ggplot2's internals regardless of implementation.

As this behaviour is intentional and not subject to any bugs, I'll close this issue here.