coverage report has no percentage data

[RwwL]

When I run yarn test, the console output shows me a coverage summary with percentages, like:

Ran all test suites.
-----------------|----------|----------|----------|----------|-------------------|
File             |  % Stmts | % Branch |  % Funcs |  % Lines | Uncovered Line #s |
-----------------|----------|----------|----------|----------|-------------------|
All files        |    38.06 |    27.91 |    13.33 |    39.68 |                   |
Comp1.jsx        |     41.3 |    32.76 |       10 |    44.19 |... 06,107,116,124 |
Comp2.jsx        |    36.36 |    17.86 |       15 |    37.35 |... 44,145,146,153 |
-----------------|----------|----------|----------|----------|-------------------|

...but when I view /coverage/lcov-report/index.html from the project root, the page lists the expected components correctly but contains no data.

( did notice there's not much activity on this project for ~2 years, so if you have a similar-but-newer one that you'd recommend, please say so.)