My Istanbul tests coverage reports zeroes

Question

Though my tests pass with mocha, my coverage is still all zeroes:

  5 passing (12ms)

-----------|---------|----------|---------|---------|-------------------
File       | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
-----------|---------|----------|---------|---------|-------------------
All files  |       0 |        0 |       0 |       0 |                   
 lib       |       0 |        0 |       0 |       0 |                   
  index.js |       0 |        0 |       0 |       0 | 3-28              
 src       |       0 |        0 |       0 |       0 |                   
  index.js |       0 |        0 |       0 |       0 | 2-20              
-----------|---------|----------|---------|---------|-------------------

My scripts section in package.json is as follows:

  "scripts": {
    "lint": "eslint ./src",
    "build": "npm run lint && babel ./src -d ./lib",
    "test": "mocha --require babel-core/register",
    "test-with-coverage": "nyc --all npm run test"
  },

My nyc section is as follows:

 "nyc": {
    "reporter": [
      "lcov",
      "text"
    ]
  }