Seems to work for me:

`index.js`:
```js
// module.exports = require('./lib/danzi');
console.log(process.env.NODE_ENV);
```

`package.json`:
```json
"test": "NODE_ENV=test ./node_modules/mocha/bin/mocha --reporter spec"
```

```bash
npm test

> danzi@0.1.2 test /Users/tom/Projects/src/node/danzi
> NODE_ENV=test ./node_modules/mocha/bin/mocha --reporter spec

test

...
```

… although I didn't include it in this pull request because `NODE_ENV` currently isn't being checked anywhere.