Core htmx Regression Tests

• supports unset on hx-select18ms ‣

  this.server.respondWith('GET', '/test', "Foo<span id='example'>Bar</span>")
  make('<form hx-select="#example">\n' +
          '      <button id="b1" hx-select="unset" hx-get="/test">Initial</button>\n' +
          '</form>')
  var btn = byId('b1')
  btn.click()
  this.server.respond()
  btn.innerText.should.equal('FooBar')