Core htmx API test

• ajax api fails when target invalid2ms ‣

  this.server.respondWith('GET', '/test', 'foo!')
  var div = make("<div id='d1'></div>")
  htmx.ajax('GET', '/test', '#d2').then(
    (value) => {
    },
    (reason) => {
      done()
    }
  )
  this.server.respond()
  div.innerHTML.should.equal('')