Stubbing out Reactive Var in Test

I am trying to test a event in a Template. Within the click event, there is a Reactive Var that gets set.

The test is blocked by the Reactive Var.

Any ideas on how I stub or mock a reactive var in a template?I tried adding it to the template (template.reactiveVar = “whatever”), but no go, as I don’t think it’s writeable.

The ?? indicate where I am wondering what to put.

it(‘sets a reactive var when a button is clicked’, function(){

    Template.button.fireEvent('click ', {
        context: { some: 'values', 'currentlySelectedEnvironment': 'sup' },
        event: {'target': {'text': 'testEnvironment', 'files': [{'type': type, 'name': name}]} },
        templateInstance:new Template('upload', function(e) {
        this.currentlySelectedEnvironment = new ReactiveVar(false)

    Template.button.fireEvent('click button', {'event': {'target': {'text': 'dataFromClick', Template.button);  
    chai.assert.equal(Template.reactiveVar, "clicked") 

‘click button’: function(evt, template){
var text =

TypeError: Cannot read property ‘set’ of undefined

Any ideas?