A jasmine matcher to assert the value of the 'selector' in a jQuery selection.

degrade-spec.js

// An App module to control feature parity amongst browsers that don't support them, HTML5 placeholder in this case.
describe("APP.Degrade", function() {

  describe('#shimPlaceholders', function() {

    it('invokes the html5 placeholder plugin on all input and textareas', function() {
      spyOn($.fn, 'placeholder');

      APP.Degrade.shimPlaceholders();

      expect($.fn.placeholder).toHaveBeenInvokedOnSelector('input, textarea');
    });

  });

});

degrade.js

(function($, APP) {
  APP.Degrade = {};

  // the function we want under test.
  APP.Degrade.shimPlaceholders = function() {
    $('input, textarea').placeholder(); // dependency: https://github.com/mathiasbynens/Placeholder-jQuery-Plugin
  };

  APP.Degrade.shimPlaceholders();
})(jQuery, APP);

matchers.js

beforeEach(function() {
  this.addMatchers({

    // yay for custom  matchers!
    toHaveBeenInvokedOnSelector: function(expected) {
      return this.actual.mostRecentCall.object.selector === expected;
    }

  });
});