Reality: repository consists of js and json files. Test files are collocated by *.test.js convention.
Requirement: repo should have *.js and *.json files, but shouldnt have *.test.js.
Problem:

• with --copy-files flag *.test.js are transpiled and copied even though babel config has ignore: [ '**/*.test.js' ].
• without --copy-files flag *.json files are left out and package breaks.

☯ npm run build -s
🎉  Successfully compiled 1 file with Babel.
🎉  Successfully compiled 1 file with Babel.
dist
├── copy
│   ├── index.js
│   ├── index.test.js
│   └── l10n.json
└── notcopy
    └── index.js
dist-expected
├── index.js
└── l10n.json