This example project demonstrates a (potential) issue with nyc source maps where the absolute source file path is incorrect.
There are two branches master and javascript.
The project uses ts-node as a mocha compiler to transpile TypeScript files when requested.
The master branch demonstrates the issue. The source file paths in the generated json files will not contain the project directory in the absolute paths. So for example, if you installed the project to ~/projects/nyc-test/ the source map path for src/calc.ts will be ~/projects/src/calc.ts and not the expected ~/projects/nyc-test/src/calc.ts.
The javascript branch simply shows that changing the src/calc.ts file to src/calc.js fixes the issue. I did also remove a TypeScript specific statement from the original src/calc.ts file - the removed statement is declare var module;. No other changes were made, for example mocha is still using ts-node as the compiler.
Install dependencies:
npm i
Run code coverage:
npm run cover
Investigate the output json files in .nyc_output. Open the json file and look at the absolute file paths.
What you will see:
~/projects/src/calc.ts
What is expected:
~/projects/nyc-test/src/calc.ts
Now switch to the javascript branch and follow the same steps. On this branch the absolute file paths will be correct.