feat: Add Typescript types to waitForElement (#21)

Fix types for Flow too

README.md

@@ -259,7 +259,7 @@ fireEvent.scroll(getByTestId('scroll-view'), eventData);
 Defined as:
 
 ```jsx
-function waitForExpect<T: ReactTestInstance>(
+function waitForExpect<T: *>(
   expectation: () => T,
   timeout: number = 4500,
   interval: number = 50

src/waitForElement.js

@@ -1,9 +1,9 @@
 // @flow
-export default function waitForExpect<T: ReactTestInstance>(
+export default function waitForExpect<T: *>(
   expectation: () => T,
   timeout: number = 4500,
   interval: number = 50
-) {
+): Promise<T> {
   const startTime = Date.now();
   return new Promise<T>((resolve, reject) => {
     const rejectOrRerun = error => {

typings/__tests__/index.test.tsx

@@ -1,6 +1,13 @@
 import * as React from 'react';
 import { ReactTestInstance } from 'react-test-renderer';
-import { render, fireEvent, shallow, flushMicrotasksQueue, debug } from '../..';
+import {
+  render,
+  fireEvent,
+  shallow,
+  flushMicrotasksQueue,
+  debug,
+  waitForElement,
+} from '../..';
 
 const View = props => props.children;
 const Text = props => props.children;
@@ -77,3 +84,10 @@ const waitForFlush: Promise<any> = flushMicrotasksQueue();
 
 debug(<TestComponent />);
 debug(getByNameString);
+
+const waitBy: Promise<ReactTestInstance> = waitForElement<ReactTestInstance>(
+  () => tree.getByName('View')
+);
+const waitByAll: Promise<Array<ReactTestInstance>> = waitForElement<
+  Array<ReactTestInstance>
+>(() => tree.getAllByName('View'), 1000, 50);

typings/index.d.ts

@@ -45,6 +45,12 @@ export type FireEventAPI = FireEventFunction & {
   scroll: (element: ReactTestInstance, data?: any) => any;
 };
 
+export type WaitForElementFunction = <T = any>(
+  expectation: () => T,
+  timeout?: number,
+  interval?: number
+) => Promise<T>;
+
 export declare const render: (
   component: React.ReactElement<any>,
   options?: RenderOptions
@@ -57,3 +63,4 @@ export declare const debug: (
   instance: ReactTestInstance | React.ReactElement<any>
 ) => void;
 export declare const fireEvent: FireEventAPI;
+export declare const waitForElement: WaitForElementFunction;