Filter and build integration tests needed only

[pickfire]

Describe the problem you are trying to solve

There is a project with 20+ integration tests, it takes like few minutes to build all of them. Even with a small change in one of the tests file and I wanted to just run one of the tests file, I did cargo tests part_a but it still compiles everything again.

The solution right now,

1. rm tests/*
2. git restore tests/part_a.rs
3. cargo test part_a, try rebuilding
4. git restore src/dep.rs, add some dependencies needed

Essentially, this will also remove the issue of clogging the screen with 0 tests run and the need to scroll up multiple times to search for the tests run #4324.

Describe the solution you'd like

Search for the functions used in the filter (cargo test <filter>), build and run only those files needed. Something like ripgrep for function name, but this requires cargo to include the dependencies too.

This provides 2 benefits, reducing the need to build unneeded files and prevent clogging the screen by running file without tests matching the filter.

Notes

I would like to take on this issue if the complexity is not high or if there are people willing to mentor.

[alexcrichton]

Thanks for the report, but cargo test part_a does not mean, to Cargo, "run the part_a test" but it instead means "pass part_a to all test executables as an argument". To run only one test you can use --test part_a, and then Cargo won't build the other targets.

[pickfire]

Ah, I did not know cargo --test part_a exists, I believe it would be nice to add an example for that. Yes, all my functions are prefixed with part_a, so cargo test part_a should work.

[ehuss]

I think this is already documented in the cargo test man page. There is an example for exactly this case at the bottom of https://doc.rust-lang.org/cargo/commands/cargo-test.html. However, I think it would be reasonable to emphasize how target selection works at the top where it introduces test filtering.

[pickfire]

Ah, I just realized it is documented in cargo test man page, I rarely read cargo man pages since it is more troublesome to read it, like I need to rustup man cargo-test rather than just alt-h in fish to show the man page since it is not in the MANPATH, so usually I just rustup test --help. Should we add rustup man pages to the MANPATH during installation?

[icorbrey]

Mind if I take a stab at this? I haven't been able to contribute to an OSS project before so I'm trying to find ways to help out. It looks like I should be able to add specific wording in src/doc/man/cargo-test.adoc to emphasize the usage of --test

[pickfire]

@icorbrey Yes, definitely. It would be good to make the wordings simpler and clearer. One thing I like is https://github.com/Dhghomon/easy_rust

[icorbrey]

I think that adding the rust manuals to the MANPATH would be good, but that's probably outside the scope of this issue lol