What is this DalekJS error stand for when I try to run a test?

I have just installed DalekJS (or at least I tried to) but it gives me the following error when I try to run a test:

Running tests
/Users/.../node_modules/dalekjs/node_modules/dalek-browser
phantomjs/index.js:273
this.spawned.kill('SIGTERM');
            ^
TypeError: Cannot read property 'kill' of null
at Object.PhantomJSDriver.kill
(/Users/.../node_modules/dalekjs/node_modules/dalek-browser-phantomjs/index.js:273:17)
at EventEmitter.emit (/Users/.../node_modules/dalekjs/node_modules/eventemitter2/lib/eventemitter2.js:312:17)
at Object.Dalek._shutdown (/Users/.../node_modules/dalekjs/lib/dalek.js:346:24)
at emitOne (events.js:77:13)
at process.emit (events.js:169:7)
at process._fatalException (node.js:211:26)

What is this trying to tell me? I have tried to reinstall it but did not help.

(Please note that I am absolutely beginner at this and I am using OS X.)