chore: exclude barrel files from coverage reporting

[kurtdoherty]

Context

In some recent work, we saw the addition of test coverage for a barrel file (a file, usually named index.ts, that simply re-exports code from other modules) in order to increase the reported coverage percentage above our minimum threshold.

As the discussion suggests, doing this is just "gaming the system." We don't want to add tests for the sake of our coverage metrics as that approach will lead to low-value, high-maintenance tests, and undermine the value coverage metrics are meant to provide: namely, the identification of possible risk in our code.

Instead of simply adding test coverage against a module that does not need tests (like barrel files), we should be assessing whether there's any meaningful coverage gaps being reported. Barrel files are not a meaningful gap.

This PR

Currently, our coverage metrics are tracking coverage for barrel files. These files will never have test coverage, so we they should not be included in our coverage reports.

The risk of excluding all index.ts files is that we do not strictly know whether the file is a barrel file, or if it does contain code we want coverage metrics for. Personally, I don't think this risk outweighs the annoyance of barrel files dragging our real coverage metrics down and would prefer to rely on the convention that index.ts files should only ever be barrel files.

This PR also scouts two issues with the recent Chip/ChipGroup work:

• The ChipGroupItem test module was incorrectly named;
• The Chip component was missing coverage for the onClick callback being called when the chip is enabled.

[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
Report missing for 9d190ef1	✅ ∅

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (9d190ef)	Report Missing	Report Missing	Report Missing
Head commit (73d28ec)	4222	3815	90.36%

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#315)	0	0	∅ (not applicable)

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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Footnotes

1. Codacy didn't receive coverage data for the commit, or there was an error processing the received data. Check your integration for errors and validate that your coverage setup is correct. ↩