docs: Add visibility example (#95)

* Create collapsible component

* Create collapsed elements visibility test

* Add why we can use getByText explanation

Author: edufarre

src/__tests__/components/Collapsible.vue

@@ -0,0 +1,23 @@
+<template>
+  <div>
+    <button @click="handleClick">Click me</button>
+    <div v-show="displayElement">
+      <p>Text</p>
+    </div>
+  </div>
+</template>
+
+<script>
+export default {
+  data() {
+    return {
+      displayElement: false,
+    }
+  },
+  methods: {
+    handleClick(e) {
+      this.displayElement = !this.displayElement
+    },
+  },
+}
+</script>

src/__tests__/visibility.js

@@ -0,0 +1,28 @@
+import {render, fireEvent} from '@testing-library/vue'
+import '@testing-library/jest-dom/extend-expect'
+import Collapsible from './components/Collapsible'
+
+// Using the query `getByText` here is completely right because
+// we use `v-show` in the component, which means that the element
+// will be rendered but not visible, whereas if we use `v-if` instead
+// we should use the `queryByText` and expect it to be `null` because
+// the element won't be rendered
+test('Collapsible component', async () => {
+  const {getByText} = render(Collapsible)
+
+  // Check that text element is not initially visible.
+  expect(getByText('Text')).not.toBeVisible()
+
+  // Click button in order to display the collapsed text element
+  const button = getByText('Click me')
+  await fireEvent.click(button)
+
+  // Check that text element is visible
+  expect(getByText('Text')).toBeVisible()
+
+  // Click button to hide the visible text element
+  await fireEvent.click(button)
+
+  // Check that text element is not visible again
+  expect(getByText('Text')).not.toBeVisible()
+})