fix(tests): expectations of some async test where not working (#989)

test/debounce.test.js

@@ -3,8 +3,10 @@ const {debounce} = require('./_30s.js');
 test('debounce is a Function', () => {
   expect(debounce).toBeInstanceOf(Function);
 });
-test('Works as expected', () => {
-  debounce(() => {
+test('Works as expected', done => {
+  const debouncedFn = debounce(() => {
     expect(true).toBeTruthy();
+    done();
   });
+  debouncedFn();
 });