I am unsure how to test my change. I think it is important someone rebuilds the docs and checks that my code block is rendered as expected.

cargo doc --no-deps --open

I would also expect no_run to be used here as the doc tests cargo test or cargo test --doc might be run on a machine without /dev/ttyS0?
Also see https://doc.rust-lang.org/rustdoc/write-documentation/documentation-tests.html.

Thank you very much for your contribution @Teufelchen1 and the fruitful discussion @EdJoPaTo! Added no_run and cleaned up the example below.

Using

$ cargo doc --no-deps --open

generates the documentation. The tests for the documentation are run along with other tests. As of 777e15b:

$ export SERIALPORT_RS_TEST_PORT_1=DUMMY_1
$ export SERIALPORT_RS_TEST_PORT_2=DUMMY_2
$ cargo test --features ignore-hardware-tests
[...]
   Doc-tests serialport

running 4 tests
test src/lib.rs - new (line 804) - compile ... ok
test src/posix/tty.rs - posix::tty::TTYPort (line 40) - compile ... ok
test src/posix/tty.rs - posix::tty::TTYPort (line 50) ... ok
test src/posix/tty.rs - posix::tty::TTYPort::pair (line 252) ... ok

test result: ok. 4 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.63s

I'm currently working on changing the configuration for the tests so that when hardware tests are ignored no environment variables need to be set. Please be patient with this work-in-progress.