(function(ns, bla) {

    ns.myMethod = function(param1) {
        //bla.callMethod();
    };

})(window.mymodule = window.mymodule || {}, bla);

describe("When the mymodule is loaded", function () {
    it("The callMethod is called", function () {
        window.bla = {
            callMethod = function() {}
        };

        expect(bla.callMethod).hasBeenCalled();  // something like this ?
    });