NUnit на моно?

function bindEvent() {
 const sliderList = document.querySelectorAll('.slider');
 [...sliderList].forEach((slider) => slider.addEventListener('click', () => {
    const left = slider.parentElement.querySelector('.switch-left');
    const right = slider.parentElement.querySelector('.switch-right');
    const leftDisplay = left.style.display || 'flex';
    const rightDisplay = right.style.display || 'none';
    left.style.display = rightDisplay;
    right.style.display = leftDisplay;
 }, false));
}

window.onload = bindEvent;

<div>
  <button class="slider"> - SLIDER 1 - </button>
  <div class="switch-left">L</div><div class="switch-right">R</div>
</div>
<div>
  <button class="slider"> - SLIDER 2 - </button>
  <div class="switch-left">L</div><div class="switch-right">R</div>
</div>
<div>
  <button class="slider"> - SLIDER 3 - </button>
  <div class="switch-left">L</div><div class="switch-right">R</div>
</div>
<div>
  <button class="slider"> - SLIDER 4 - </button>
  <div class="switch-left">L</div><div class="switch-right">R</div>
</div>