Enzyme simulate an onChange event
You can simply spy to the method directly via the prototype.
it("responds to name change", done => { const handleChangeSpy = sinon.spy(New.prototype, "handleChange"); const event = {target: {name: "pollName", value: "spam"}}; const wrap = mount( <New /> ); wrap.ref('pollName').simulate('change', event); expect(handleChangeSpy.calledOnce).to.equal(true);})Alternatively, you can use spy on the instance's method, but you have to make a forced update because the component is already rendered after mount is called, which means the onChange is already bound to its original.
it("responds to name change", done => { const event = {target: {name: "pollName", value: "spam"}}; const wrap = mount( <New /> ); const handleChangeSpy = sinon.spy(wrap.instance(), "handleChange"); wrap.update(); // Force re-render wrap.ref('pollName').simulate('change', event); expect(handleChangeSpy.calledOnce).to.equal(true);})