nyc@7.1.0 working demo

package.json

{
  "name": "nyc-ava-test",
  "version": "1.0.0",
  "main": "say.js",
  "scripts": {
    "test": "cross-env NODE_ENV=test nyc ava"
  },
  "license": "ISC",
  "babel": {
    "presets": [
      "es2015"
    ],
    "env": {
      "test": {
        "plugins": [
          "istanbul"
        ]
      }
    }
  },
  "ava": {
    "require": [
      "babel-register"
    ]
  },
  "nyc": {
    "require": [
      "babel-register"
    ],
    "reporter": [
      "lcov",
      "text-summary"
    ],
    "sourceMap": false,
    "instrument": false
  },
  "devDependencies": {
    "ava": "^0.15.1",
    "babel": "^6.5.2",
    "babel-cli": "^6.9.0",
    "babel-plugin-istanbul": "^1.0.1",
    "babel-preset-es2015": "^6.9.0",
    "babel-register": "^6.9.0",
    "cross-env": "^1.0.8",
    "nyc": "^7.1.0"
  }
}

say.js

module.exports = function say({
  greeting = 'Hello',
  noun = 'world'
} = {}) {
  return greeting + ' ' + noun;
}

test.js

import test from 'ava';
import say from './say';

test('should default to hello world', t => {
  t.is(say(), 'Hello world');
});

test('should say a custom greeting to hello world', t => {
  t.is(say({
    greeting: 'Hi',
    noun: 'Phil'
  }), 'Hi Phil');
});