Is this a bug report?

Yes.

Can you also reproduce the problem with npm 4.x?

No.

Which terms did you search for in User Guide?

• istanbul
• metrics.isEmpty
• coverage

Environment

1. npm ls react-scripts-ts (if you haven’t ejected): react-scripts-ts@2.14.0
2. node -v: v9.10.0
3. npm -v: 5.8.0
4. yarn --version (if you use Yarn): 1.3.2
5. npm ls react-scripts-ts (if you haven’t ejected): react-scripts-ts@2.14.0

Then, specify:

1. Operating system: macOS Version 10.12 / Windows 10

Steps to Reproduce

1. Install react-scripts-ts in version 2.14 (no issues in version 2.13)
2. Run npm run test or yarn test (runs jest with --coverage)

Expected Behavior

The tool writes the coverage report.

Actual Behavior

The tool doesn't write the coverage report.
Stacktrace below:

        Failed to write coverage reports:
        ERROR: TypeError: metrics.isEmpty is not a function
        STACK: TypeError: metrics.isEmpty is not a function
    at tableRow (/UserPath/ts-coverage-error/node_modules/istanbul-reports/lib/text/index.js:133:27)
    at TextReport.onSummary (/UserPath/ts-coverage-error/node_modules/istanbul-reports/lib/text/index.js:188:15)
    at TextReport.onDetail (/UserPath/ts-coverage-error/node_modules/istanbul-reports/lib/text/index.js:193:17)
    at Visitor.(anonymous function) [as onDetail] (/UserPath/ts-coverage-error/node_modules/istanbul-lib-report/lib/tree.js:34:30)
    at ReportNode.Node.visit (/UserPath/ts-coverage-error/node_modules/istanbul-lib-report/lib/tree.js:123:17)
    at /UserPath/ts-coverage-error/node_modules/istanbul-lib-report/lib/tree.js:116:23
    at Array.forEach (<anonymous>)
    at visitChildren (/UserPath/ts-coverage-error/node_modules/istanbul-lib-report/lib/tree.js:115:32)
    at ReportNode.Node.visit (/UserPath/ts-coverage-error/node_modules/istanbul-lib-report/lib/tree.js:126:5)
    at /UserPath/ts-coverage-error/node_modules/istanbul-lib-report/lib/tree.js:116:23

Reproducible Demo

Demo Project

1. clone the project
2. run yarn
3. run yarn test / npm run test

If I delete my node_modules rm -rf node_modules then run npm install and npm test/yarn test it works. (at least on my computer, couldn't reproduce this in my CI.)
And if I downgrade to react-scripts-ts 2.13.0 and re-run yarn + yarn test there's also no metrics.isEmpty is not a function error.

Hope you can reproduce this issue and find out why it happens. I find it really weird!