Error: You attempted to overwrite the built-in helper "array". Where is this coming from?

How do I track down where this error is coming from? I searched my own codebase, and could not find anywhere that I was using the helper. It happens during an acceptance test.

You attempted to overwrite the built-in helper "array" which is not allowed. Please rename the helper.

I am attempting to update some of my Ember dependencies, which surfaced this problem.