Test files in different places: is it on purpose?

[GegznaV]

Some files are in tests/testthat/ others are in inst/extdata/ directory.

Is this on purpose or accidentally?

As I understand, files in inst/extdata/ can be used in both tests and examples but count to the size of the installed R package.

And what's about tests/testthat/: do files in this directory count to the size of the installed package?
R finds these files when devtools::test() is called but there is an issue to run tests manually.