How do you mock directives to enable unit testing of higher level directive?

Directives are just factories, so the best way to do this is to mock the factory of the directive in using the module function, typically in the beforeEach block. Assuming you have a directive named do-something used by a directive called do-something-else you’d mock it as such:

beforeEach(module('yourapp/test', function($provide){
  $provide.factory('doSomethingDirective', function(){ return {}; });
}));

// Or using the shorthand sytax
beforeEach(module('yourapp/test', { doSomethingDirective: {} ));

Then the directive will be overridden when the template is compiled in your test

inject(function($compile, $rootScope){
  $compile('<do-something-else></do-something-else>', $rootScope.$new());
});

Note that you need to add the ‘Directive’ suffix to the name because the compiler does this internally: https://github.com/angular/angular.js/blob/821ed310a75719765448e8b15e3a56f0389107a5/src/ng/compile.js#L530