nyc is able to show you all Node processes that are spawned when running a test script under it:
$ nyc --show-process-tree npm test
3 passed
----------|----------|----------|----------|----------|----------------|
File | % Stmts | % Branch | % Funcs | % Lines |Uncovered Lines |
----------|----------|----------|----------|----------|----------------|
All files | 100 | 100 | 100 | 100 | |
index.js | 100 | 100 | 100 | 100 | |
----------|----------|----------|----------|----------|----------------|
nyc
└─┬ /usr/local/bin/node /usr/local/bin/npm test
└─┬ /usr/local/bin/node /path/to/your/project/node_modules/.bin/ava
└── /usr/local/bin/node /path/to/your/project/node_modules/ava/lib/test-worker.js …