One way is to define a new module (e.g. 'specApp') that declares your app (e.g. 'myApp') as a dependency. Then register a 'customerController' controller with the 'specApp' module. This will effectively "hide" the customerController of 'myApp' and supply this mock-controller to the directive when compiled.
E.g.:
Your app:
var app = angular.module('myApp', []);
...
app.controller('customerController', function ($scope,...) {
$scope = {...};
...
});
app.directive('myCustomer', function () {
return {
template: 'cust.html',
controller: 'customerController'
};
});
Your spec:
describe('"myCustomer" directive', function () {
$compile;
$newScope;
angular.module('specApp', ['myApp'])
/* Register a "new" customerController, which will "hide" that of 'myApp' */
.controller('customerController', function ($scope,...) {
$scope = {...};
...
});
beforeEach(module('specApp'));
it('should do cool stuff', function () {
var elem = angular.element('<div my-customer></div>');
$compile(elem)($newScope);
$newScope.$digest();
expect(...
});
});
See, also, this working demo.