Core htmx client side validation tests

• Custom validation error prevents request14ms ‣

  this.server.respondWith('POST', '/test', 'Clicked!')
  var form = make('<form hx-post="/test" hx-trigger="click">' +
          'No Request' +
          '<input id="i1" name="i1">' +
          '</form>')
  byId('i1').setCustomValidity('Nope')
  form.textContent.should.equal('No Request')
  form.click()
  this.server.respond()
  form.textContent.should.equal('No Request')
  byId('i1').setCustomValidity('')
  form.click()
  this.server.respond()
  form.textContent.should.equal('Clicked!')