Additional tests

test/insertBefore.test.js

@@ -4,3 +4,10 @@ const {insertBefore} = require('./_30s.js');
 test('insertBefore is a Function', () => {
   expect(insertBefore).toBeInstanceOf(Function);
 });
+let e = document.createElement('div');
+e.setAttribute("id", "test");
+test('Does not throw error if the element exists', () => {
+  expect(() => {
+    insertBefore(e, '<span>test</span>');
+  }).not.toThrow(TypeError);
+});