Prevent duplicate $digest calls

Hello. Having some trouble here with a Jasmine test...

I'm testing an API service that uses ```$http```, and mocking the backend with ```$httpBackend```.

The test looks like this:

```javascript
/// api.js

.
.
.

describe('API #get()', function () {

    afterEach(function () {
      $httpBackend.verifyNoOutstandingRequest();
      $httpBackend.verifyNoOutstandingExpectation(); // LINE 33
    });

    it('should return something falsy when the server does', function (done) {
      $httpBackend.expect('GET', 'http://api.example.com/')
        .respond({
          'code': '200',
          'data': {
            'valid': false
          }
        });

      API.get()
        .then(function (valid) {
          expect(valid).toBeFalsy();
          done(); // LINE 52
        });

      $httpBackend.flush(); // LINE 55
    });

  });

});

.
.
.
```

And here's the stack trace. I labeled the notable lines in ```api.js``` above with a comment.

```
  Error: [$rootScope:inprog] $digest already in progress
  http://errors.angularjs.org/1.2.12/$rootScope/inprog?p0=%24digest
      at beginPhase (.../app/bower_components/angular/angular.js:12290)
      at .../app/bower_components/angular/angular.js:11792
      at .../app/bower_components/angular-mocks/angular-mocks.js:1484
      at .../test/spec/services/api.js:33
      at .../test/spec/services/api.js:52
      at .../app/bower_components/angular/angular.js:10965
      at .../app/bower_components/angular/angular.js:11051
      at .../app/bower_components/angular/angular.js:11977
      at .../app/bower_components/angular/angular.js:11803
      at .../app/bower_components/angular/angular.js:12083
      at done (.../app/bower_components/angular/angular.js:7841)
      at handleResponse (.../app/bower_components/angular-mocks/angular-mocks.js:1130)
      at .../app/bower_components/angular-mocks/angular-mocks.js:1461
      at .../test/spec/services/api.js:55
```

The change that I'm PRing seems to fix everything (hopefully!), but I'm sure the experts have something different to say... (I'm doing this all wrong?)

Thanks for your time!