Why does a model test have to be in an Ember.run block when it is only testing computed properties?

I have a model (DS.Model) with a few computed properties and it has a custom adapter that extends DS.Adapter. Nothing asynchronous that I know of is going on here, but in my qUnit test I get the error pasted below. It is fixed if I wrap my assertion in an Ember.run() block. Does anyone know why?

Error: Assertion Failed: You have turned on testing mode, which disabled the run-loop's autorun. You will need to wrap any code with asynchronous side-effects in a run at new Error (native)