每个钩子错误之前的角度业力幻像

我正在使用业力和幻影运行我的测试,我正在使用mocha和sinon,有时测试通过,有时我没有任何理由得到这个错误:

    ? "before each" hook: workFn
      ? should call get user api
  ? "after each" hook for "should call get user api"

Finished in 1.04 secs / 0.2 secs

SUMMARY:
? 42 tests completed
? 3 tests failed

FAILED TESTS:
  UserService
    ? "before each" hook: workFn
      PhantomJS 1.9.8 (Mac OS X 0.0.0)
    TypeError: 'null' is not an object (evaluating 'document.querySelector('.arrow' + index).classList') (public/client/build/main.js:3195)

  ? "after each" hook for "should call get user api"
    PhantomJS 1.9.8 (Mac OS X 0.0.0)
    PhantomJS 1.9.8 (Mac OS X 0.0.0)
  TypeError: 'null' is not an object (evaluating 'currentSpec.$injector')
      at public/vendor/angular-mocks/angular-mocks.js:2229

什么可以导致这个问题？