add getClosestElement tests

src/__tests__/helpers/getClosestElement.test.js

@@ -0,0 +1,27 @@
+import getClosestElement from '../../helpers/getClosestElement'
+
+const template = `
+<div class="outer">
+  <div class="inner">
+    <span class="element"></span>
+  </div>
+</div>
+`
+
+document.body.innerHTML = template
+const element = document.querySelector('.element')
+
+describe('getClosestElement', () => {
+  it('should return the closest matching ancestor', () => {
+    const ancestor = getClosestElement(element, 'div')
+
+    expect(ancestor.classList).toContain('inner')
+  })
+
+  it('should return null if there isn\'t a matching ancestor', () => {
+    const ancestor = getClosestElement(element, 'section')
+
+    expect(ancestor).toBeNull()
+  })
+
+})