Empty coverage is not generated correctly

[mengdage]

🐛 Bug Report

When a file is not covered by any unit tests, jest consider it as a untested file and generate empty coverage for it. However, these files are instrumented by babel without using babel-plugin-istanbul. Therefore, if they use ES6. The coverage data is not correct.

To Reproduce

I created a repo to reproduce the bug. https://github.com/mengdage/jest-empty-coverage-bug

In that repo, the file BrandTable.jsx uses ES6 and the empty coverage generated for it is not correct.

Expected behavior

The empty coverage for BrandTable.jsx is incorrect.

Link to repl or repo (highly encouraged)

https://github.com/mengdage/jest-empty-coverage-bug

[mengdage]

I am working on a solution. See this PR for details. It fixes my problem. But I'm not sure if it would break anything because the I don't fully understand the purpose of the original code. Why does it choose not instrumenting the code when transforming, and then instrument it afterwards?

[github-actions]

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