Add section on how to write tests and run tests for the ratatui library

[kdheepak]

In the developer guide, we should add a section on how to write tests and run tests.

This section should include a brief primer on cargo test, e.g.:

1. To run tests, you can use cargo test but if you want to print to stdout, you can use -- --nocapture.
2. If you only want to run tests in the library, you can use --lib flag.
3. If you want to run a subset of tests, you can add a test name that will match for all the functions by the same name.

e.g.

cargo test --lib test_render -- --nocapture

We also also add instructions for cargo nextest and how to run a subset of tests using that.

In terms of writing tests, some modules use rstest, which can make writing a series of specification tests like so quite easily to parse:

mod tests {
        use rstest::rstest;

        #[rstest]
        #[case(Flex::Legacy, 1, &[Min(0), Min(0)], "b")] // zero, zero
        #[case(Flex::Legacy, 1, &[Min(0), Min(1)], "b")] // zero, exact
        #[case(Flex::Legacy, 1, &[Min(0), Min(2)], "b")] // zero, overflow
        #[case(Flex::Legacy, 1, &[Min(1), Min(0)], "a")] // exact, zero
        #[case(Flex::Legacy, 1, &[Min(1), Min(1)], "a")] // exact, exact
        #[case(Flex::Legacy, 1, &[Min(1), Min(2)], "a")] // exact, overflow
        #[case(Flex::Legacy, 1, &[Min(2), Min(0)], "a")] // overflow, zero
        #[case(Flex::Legacy, 1, &[Min(2), Min(1)], "a")] // overflow, exact
        #[case(Flex::Legacy, 1, &[Min(2), Min(2)], "a")] // overflow, overflow
        #[case(Flex::Legacy, 2, &[Min(0), Min(0)], "bb")] // zero, zero
        #[case(Flex::Legacy, 2, &[Min(0), Min(1)], "bb")] // zero, underflow
        #[case(Flex::Legacy, 2, &[Min(0), Min(2)], "bb")] // zero, exact
        #[case(Flex::Legacy, 2, &[Min(0), Min(3)], "bb")] // zero, overflow
        #[case(Flex::Legacy, 2, &[Min(1), Min(0)], "ab")] // underflow, zero
        #[case(Flex::Legacy, 2, &[Min(1), Min(1)], "ab")] // underflow, underflow
        #[case(Flex::Legacy, 2, &[Min(1), Min(2)], "ab")] // underflow, exact
        #[case(Flex::Legacy, 2, &[Min(1), Min(3)], "ab")] // underflow, overflow
        #[case(Flex::Legacy, 2, &[Min(2), Min(0)], "aa")] // exact, zero
        #[case(Flex::Legacy, 2, &[Min(2), Min(1)], "aa")] // exact, underflow
        #[case(Flex::Legacy, 2, &[Min(2), Min(2)], "aa")] // exact, exact
        #[case(Flex::Legacy, 2, &[Min(2), Min(3)], "aa")] // exact, overflow
        #[case(Flex::Legacy, 2, &[Min(3), Min(0)], "aa")] // overflow, zero
        #[case(Flex::Legacy, 2, &[Min(3), Min(1)], "aa")] // overflow, underflow
        #[case(Flex::Legacy, 2, &[Min(3), Min(2)], "aa")] // overflow, exact
        #[case(Flex::Legacy, 2, &[Min(3), Min(3)], "aa")] // overflow, overflow
        #[case(Flex::Legacy, 3, &[Min(2), Min(2)], "aab")]
        fn min(
            #[case] flex: Flex,
            #[case] width: u16,
            #[case] constraints: &[Constraint],
            #[case] expected: &str,
        ) {
            letters(flex, constraints, width, expected);
        }
}

This use the rstest crate. A specific case from a test can be run by using something like the following:

cargo test --lib -- tests::min::case_08 --nocapture

Sometimes, the case has more information in the name like in this section and then to run case 08 you can do this:

cargo test --lib -- layout::layout::tests::split::length_is_higher_priority_in_flex::case_08_length_higher_priority --nocapture

[kdheepak]

Possibly related to #358

[EdJoPaTo]

We also also add instructions for cargo nextest and how to run a subset of tests using that.

Personally I would try to explain everything for cargo test too. As long as it works with standard. nextest might execute faster but is not part of the default cargo experience which people are familiar with. As long as it works with the standard tools without installing anything additionally we should keep that working to reduce the entry barrier.

---

Side note… git config --global core.hooksPath /dev/null was one of the best things I did since I worked on ratatui… I don't have cargo-make installed anymore too. Only typos is remaining for my local setup.

[joshka]

Side note… git config --global core.hooksPath /dev/null was one of the best things I did since I worked on ratatui… I don't have cargo-make installed anymore too. Only typos is remaining for my local setup.

Yeah, I often git push --no-verify before I create a PR (gh pr create) to avoid the time suck of running the CI while pushing too. We should definitely shorten that process a whole bunch to avoid it being a papercut that gets turned off.