How to test style for a React component attribute with Enzyme

const elem = wrapper.find(Element);
expect(getComputedStyle(elem.getDOMNode()).getPropertyValue('opacity')).toBe('0.4');

expect(component.find('#item-id').prop('style')).to.deep.equal({display: 'none'})

You can use this method. It returns ReactElement.

let containerStyle = container.get(0).style;
expect(containerStyle).to.have.property('opacity', '1');

Slightly elaborating on others' answers:

expect(component.find('#item-id').prop('style')).toHaveProperty('backgroundSize', '100%');

This will check the style prop of #item-id. This prop is an object and here toHaveProperty matcher checks if this object contains backgroundSize property and if its value is 100%.

This way other style properties are ignored.