How to stub filter with Angular and Karma

test.coffee

$filter = undefined

beforeEach ->
  angular.mock.module ($provide) ->
    $provide.value "translateFilter", (key) ->
      "TRANSLATED_#{key}"
      
    # Without explicitly returning or returning "null" it raises error
    # https://groups.google.com/forum/#!msg/angular/gCGF_B4eQkc/XjkvbgE9iMcJ
    return
    
  inject ($injector) ->
    $filter = $injector.get("$filter")
    
it "returns value from mocked filter", ->
  expect($filter("translate")("whatever")).toEqual("TRANSLATED_whatever")