nodemon error when watching files for Jasmine testing on node.js project

I'm using Jasmine 2.5.3 and nodemon 1.11.0. In my package.json I have:

"scripts": {
    "test": "nodemon --exec jasmine,
    ...
}

When I run npm test command, it watches for file changes as I'd expect, but each time it runs the tests it then prints:

[nodemon] app crashed - waiting for file changes before starting...

The app itself definitely doesn't crash, so I'm wondering what is causing this error, and how I can get it to go away.

via BarthesSimpson