How to test AngularJS custom provider

I had this same question and only found a working solution in this Google Group answer and it’s referenced fiddle example.

Testing your provider code would look something like this (following the code in the fiddle example and what worked for me):

describe('Test app.config provider', function () {

    var theConfigProvider;

    beforeEach(function () {
        // Initialize the service provider 
        // by injecting it to a fake module's config block
        var fakeModule = angular.module('test.app.config', function () {});
        fakeModule.config( function (configProvider) {
            theConfigProvider = configProvider;
        });
        // Initialize test.app injector
        module('app.config', 'test.app.config');

        // Kickstart the injectors previously registered 
        // with calls to angular.mock.module
        inject(function () {});
    });

    describe('with custom configuration', function () {
        it('tests the providers internal function', function () {
            // check sanity
            expect(theConfigProvider).not.toBeUndefined();
            // configure the provider
            theConfigProvider.mode('local');
            // test an instance of the provider for 
            // the custom configuration changes
            expect(theConfigProvider.$get().mode).toBe('local');
        });
    });

});