Update resolveThunk.js

Author: migueloller

src/build/__tests__/resolveThunk-test.js

@@ -1,9 +1,9 @@
-/* eslint-env jest */
+/* @flow */
 
 import resolveThunk from '../resolveThunk';
 
 describe('resolveThunk()', () => {
-  it('should work', () => {
+  test('works', () => {
     expect(resolveThunk(true)).toBe(true);
     expect(resolveThunk(() => true)).toBe(true);
   });

src/build/resolveThunk.js

@@ -1,3 +1,7 @@
-export default function resolveThunk(thunk) {
+/* @flow */
+
+export type Thunk<T> = (() => T) | T;
+
+export default function resolveThunk<T>(thunk: Thunk<T>): T {
   return typeof thunk === 'function' ? thunk() : thunk;
 }