Add support for global and group slot numbers

[sunshowers]

Per #2142 -- add support for global and group slots.

This should address a class of problems around things like port number allocations. For example, if you want to reserve blocks of 5 ports for tests, you could pick an arbitrary starting port in the ephemeral port range (e.g. 46210) and then do starting_port + 5 * NEXTEST_TEST_GROUP_SLOT.

These slots are numbers increasing from 0, are unique for the lifetime of the test within the nextest run (or within the group), and are compact (numbers are freed as tests finish, and the smallest possible number is always assigned to new tests).

[codecov]

Codecov Report

Attention: Patch coverage is 83.33333% with 9 lines in your changes missing coverage. Please review.

Project coverage is 80.11%. Comparing base (ffd6a8c) to head (938c5f1).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
nextest-runner/src/runner/imp.rs	89.36%	5 Missing ⚠️
nextest-runner/src/runner/executor.rs	40.00%	3 Missing ⚠️
nextest-runner/src/config/test_group.rs	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2145      +/-   ##
==========================================
- Coverage   80.12%   80.11%   -0.02%     
==========================================
  Files         103      103              
  Lines       24343    24370      +27     
==========================================
+ Hits        19505    19524      +19     
- Misses       4838     4846       +8     

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[trunk-io]

     

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[sondrelg]

Thanks again for adding this @sunshowers!

I tried cloning and checking out 9977b2a; building a release version, then running the following test:

#[test]
fn l() {
    println!("{}", std::env::var("NEXTEST_TEST_GROUP_SLOT").unwrap());
}

with ./nextest/target/release/cargo-nextest nextest run tests::l

Unexpectedly, the test fails, since the env var is undefined:

──── STDERR:             print tests::l
thread 'tests::l' panicked at src/lib.rs:142:60:
called `Result::unwrap()` on an `Err` value: NotPresent
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

  Cancelling due to test failure
────────────
     Summary [   0.011s] 1 test run: 0 passed, 1 failed, 35 skipped
        FAIL [   0.009s] print tests::l
error: test run failed

Am I doing something wrong?

--

EDIT: I typoed NEXTEST_TEST_GLOBAL_SLOT 🙈 Running three concurrent tests, I see 0, 1, and 2 for NEXTEST_TEST_GROUP 🥳

[sunshowers]

Thanks for testing it out! This suggests that merely removing the GROUP variables from the environment isn't enough, we should probably set them to values which indicate that the test is not in a group.