PropTypes.emberArray.isRequired is undefined in test env

[ArnaudValensi]

Hi!

PropTypes.emberArray.isRequired is undefined in test env

I get the following:

testem.js:1025 TypeError: Cannot read property 'isRequired' of undefined
    at Module.callback (component.js:4)
    at Module.exports (loader.js:106)
    at requireModule (loader.js:27)
    at Class._extractDefaultExport (resolver.js:382)
    at Class.resolveOther (resolver.js:79)
    at Class.superWrapper (ember.debug.js:40872)
    at Class.resolve (ember.debug.js:5317)
    at resolve (ember.debug.js:2713)
    at Registry.resolve (ember.debug.js:2172)
    at Registry.resolve (ember.debug.js:2176)

• OS: macOS Sierra 10.13.3
• Ember CLI 2.12.2
• Node 8.8.0 with npm 5.6.0
• Browser: Chrome 64.0.3282.167