Is it possible to override constants for module config functions in tests?

First of all: it seems that jasmine is not working properly in your plunkr. But I am not quite sure – maybe someone else can check this again. Nevertheless I have created a new plunkr (http://plnkr.co/edit/MkUjSLIyWbj5A2Vy6h61?p=preview) and followed these instructions: https://github.com/searls/jasmine-all.

You will see that your beforeEach code will never run. You can check this:

module(function($provide) {  console.log('you will never see this');  $provide.constant('I18n', { FOO: "bar"});});

You need two things:

1. A real test in the it function – expect(true).toBe(true) is good enough

2. You must use inject somewhere in your test, otherwise the function provided to module will not be called and the constant will not be set.

If you run this code you will see "green":

var common = angular.module('common', []);common.constant('I18n', 'foo');common.config(['I18n', function(I18n) {  console.log("common I18n " + I18n)}]);var app = angular.module('plunker', ['common']);app.config(['I18n', function(I18n) {  console.log("plunker I18n " + I18n)}]);describe('tests', function() {  beforeEach(module('common'));  beforeEach(function() {    module(function($provide) {      console.log('change to bar');      $provide.constant('I18n', 'bar');    });  });  beforeEach(module('plunker'));      it('anything looks great', inject(function($injector) {      var i18n = $injector.get('I18n');      expect(i18n).toBe('bar');  }));});

I hope it will work as you expect!

I think the fundamental issue is you are defining the constants right before the config block, so each time the module is loaded, whatever mock value that may exist will be overridden. My suggestion would be to separate out the constants and config into separate modules.

Although it seems like you can't change which object a AngularJS constant refers to after it's been defined, you can change properties of the object itself.

So in your case you can inject I18n as you would any other dependency, and then alter it before your test.

var I18n;beforeEach(inject(function (_I18n_) {  I18n = _I18n_;});describe('A test that needs a different value of I18n.foo', function() {  var originalFoo;  beforeEach(function() {    originalFoo = I18n.foo;    I18n.foo = 'mock-foo';  });  it('should do something', function() {    // Test that depends on different value of I18n.foo;    expect(....);  });  afterEach(function() {    I18n.foo = originalFoo;  });});

As above, you should save the original state of the constant, and restore it after the test, to make sure that this test doesn't interfere with any others that you might have, now, or in the future.