Ember js Mocha Testing

I have my div like this in the integration test I need to check that how many elements or length is there with class = "highcharts-grid-line" . or how many children are there with that class in ember mocha test for the div with data-test-id = "bar-chart-body".Please help to to find syntax.

It must be like expect($(.....).to.be.length(x);