Have you ever had the experience of having many subtests in a single test file, making it difficult to see the test results for the parts you want to check?

With Test2::Plugin::SubtestFilter, you can run only specific subtests. This is similar to vitest's --testNamePattern or go test's -run flag in other languages.

If you use Test2::Plugin::SubtestFilter, only subtests matching the SUBTEST_FILTER environment variable will be executed. For example, given the following test file, if you specify only_run_this in SUBTEST_FILTER, only only_run_this will be executed, and do_not_run will be skipped.

use Test2::V0;
use Test2::Plugin::SubtestFilter;

subtest 'only_run_this' => sub {
    pass;
};

subtest 'do_not_run' => sub {
    pass;
};

done_testing;

Run the test like this:

% SUBTEST_FILTER=only_run_this prove -lvr t/test.t
# => Test `only_run_this` / Skip `do_not_run`

Tips: VSCode Extension

With the following VSCode extension, you can run tests simply by clicking the run icon for test execution. How convenient!

VSCode Extension: Perl Test

Tips: Prompt for Coding Agents

If you give a coding agent a prompt like the following, it will use SUBTEST_FILTER. By narrowing down the test results to only the areas of interest, you get the benefit of reducing context consumption.

### Test Execution Rules (Required)

**When adding or modifying functions or subtests, always use
`SUBTEST_FILTER` to run only the relevant subtest.**

Example: When adding a `power` function
```bash
# Good: Run only the relevant subtest
SUBTEST_FILTER=power prove t/Hello/Math.t

# Bad: Run all tests (slow, adds noise from unrelated tests)
prove t/Hello/Math.t
```

Run all tests (`prove t/`) only in the following cases:
- When the user explicitly requests a full test run
- When making broad changes such as refactoring
- As a final check before committing

That's all. Please give it a try. Happy testing!