Added Jest Cheat Sheet in draft as .md format

Author: shahriarAS

data/draft/jest.md

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+---
+id: jest
+title: জেস্ট
+slug: jest
+description: জেস্ট একটি অত্যন্ত সহজ এবং অসাধারণ জাভাস্ক্রিপ্ট টেস্ট ফ্রেমওয়ার্ক
+colorPref: #333
+---
+
+## টেস্টিং
+
+
+
+### শুরু করার জন্য
+
+
+
+```bash
+yarn add --save-dev jest babel-jest
+```
+
+
+
+```js
+/* Add to package.json */
+"scripts": {
+  "test": "jest"
+}
+```
+
+```bash
+# Run your tests
+yarn test -- --watch
+```
+
+দেখুনঃ [Getting started](http://facebook.github.io/jest/docs/en/getting-started.html)
+
+### টেস্ট লেখার জন্য
+
+```js
+describe("My work", () => {
+  test("works", () => {
+    expect(2).toEqual(2);
+  });
+});
+```
+
+দেখুনঃ [describe()](http://facebook.github.io/jest/docs/en/api.html#describename-fn), [test()](http://facebook.github.io/jest/docs/en/api.html#testname-fn), [expect()](http://facebook.github.io/jest/docs/en/expect.html#content)
+
+### BDD সিনট্যাক্স
+
+```js
+describe('My work', () => {
+  it('works', () => {
+    ···
+  })
+})
+```
+
+`it` is an alias for `test`.
+দেখুনঃ [test()](http://facebook.github.io/jest/docs/en/api.html#testname-fn)
+
+### সেটাপ
+
+```js
+beforeEach(() => { ... })
+afterEach(() => { ... })
+```
+
+```js
+beforeAll(() => { ... })
+afterAll(() => { ... })
+```
+
+দেখুনঃ [afterAll() and more](http://facebook.github.io/jest/docs/en/api.html#afterallfn)
+
+### টেস্ট ফোকাসিং
+
+```js
+describe.only(···)
+it.only(···) // alias: fit()
+```
+
+দেখুনঃ [test.only](http://facebook.github.io/jest/docs/en/api.html#testonlyname-fn)
+
+### স্কিপিং টেস্ট
+
+```js
+describe.skip(···)
+it.skip(···) // alias: xit()
+```
+
+দেখুনঃ [test.skip](http://facebook.github.io/jest/docs/en/api.html#testskipname-fn)
+
+### অপশনাল ফ্ল্যাগ
+
+#### `--coverage` = See a summary of test coverage
+#### `--detectOpenHandles` = See a summary of ports that didn't close
+#### `--runInBand` = Run all tests one after the other
+
+
+## এক্সপেক্ট
+
+
+### ব্যাসিক এক্সপেকটেশন
+
+```js
+expect(value).not.toBe(value).toEqual(value).toBeTruthy();
+```
+
+Note that `toEqual` is a deep equality check.
+দেখুনঃ [expect()](http://facebook.github.io/jest/docs/en/expect.html#expectvalue)
+
+### স্ন্যাপশটস
+
+```js
+expect(value).toMatchSnapshot().toMatchInlineSnapshot();
+```
+
+Note that `toMatchInlineSnapshot()` requires Prettier to be set up for the project.
+দেখুনঃ [Inline snapshots](https://jestjs.io/docs/en/snapshot-testing#inline-snapshots)
+
+### ইরোর
+
+```js
+expect(value).toThrow(error).toThrowErrorMatchingSnapshot();
+```
+
+### বুলিয়ান
+
+```js
+expect(value).toBeFalsy().toBeNull().toBeTruthy().toBeUndefined().toBeDefined();
+```
+
+### নাম্বার
+
+```js
+expect(value)
+  .toBeCloseTo(number, numDigits)
+  .toBeGreaterThan(number)
+  .toBeGreaterThanOrEqual(number)
+  .toBeLessThan(number)
+  .toBeLessThanOrEqual(number);
+```
+
+### অবজেক্ট
+
+```js
+expect(value)
+  .toBeInstanceOf(Class)
+  .toMatchObject(object)
+  .toHaveProperty(keyPath, value);
+```
+
+### অব্জেক্টস
+
+```js
+expect(value).toContain(item).toContainEqual(item).toHaveLength(number);
+```
+
+### স্ট্রিং
+
+```js
+expect(value).toMatch(regexpOrString);
+```
+
+### অন্যান্য
+
+```js
+expect.extend(matchers);
+expect.any(constructor);
+expect.addSnapshotSerializer(serializer);
+
+expect.assertions(1);
+```
+
+## আরো ফিচার
+
+### অ্যাসিক্রোনাস টেস্ট
+
+```js
+test('works with promises', () => {
+  return new Promise((resolve, reject) => {
+    ···
+  })
+})
+```
+
+
+
+```js
+test('works with async/await', async () => {
+  const hello = await foo()
+  ···
+})
+```
+
+
+
+Return promises, or use async/await.
+দেখুনঃ [Async tutorial](http://facebook.github.io/jest/docs/en/tutorial-async.html)
+
+### স্ন্যাপশট
+
+```jsx
+it("works", () => {
+  const output = something();
+  expect(output).toMatchSnapshot();
+});
+```
+
+
+
+First run creates a snapshot. Subsequent runs match the saved snapshot.
+দেখুনঃ [Snapshot testing](http://facebook.github.io/jest/docs/en/snapshot-testing.html)
+
+### রিয়াক্ট টেস্ট রেন্ডারার
+
+```jsx
+import renderer from "react-test-renderer";
+```
+
+
+
+```jsx
+it("works", () => {
+  const tree = renderer
+    .create(<Link page="http://www.facebook.com">Facebook</Link>)
+    .toJSON();
+
+  expect(tree).toMatchSnapshot();
+});
+```
+
+
+
+React's test renderer can be used for Jest snapshots.
+দেখুনঃ [Snapshot test](http://facebook.github.io/jest/docs/en/tutorial-react-native.html#snapshot-test)
+
+### টাইমার
+
+```js
+jest.useFakeTimers();
+```
+
+```js
+it("works", () => {
+  jest.runOnlyPendingTimers();
+  jest.runTimersToTime(1000);
+  jest.runAllTimers();
+});
+```
+
+দেখুনঃ [Timer Mocks](http://facebook.github.io/jest/docs/en/timer-mocks.html)
+
+## মক ফাংশন
+
+### মক ফাংশন
+
+```js
+const fn = jest.fn();
+```
+
+```js
+const fn = jest.fn((n) => n * n);
+```
+
+দেখুনঃ [Mock functions](http://facebook.github.io/jest/docs/en/mock-functions.html#using-a-mock-function)
+
+### অ্যাসারশন
+
+```js
+expect(fn)
+  .toHaveBeenCalled()
+  .toHaveBeenCalledTimes(number)
+  .toHaveBeenCalledWith(arg1, arg2, ...)
+  .toHaveBeenLastCalledWith(arg1, arg2, ...)
+```
+
+```js
+expect(fn)
+  .toHaveBeenCalledWith(expect.anything())
+  .toHaveBeenCalledWith(expect.any(constructor))
+  .toHaveBeenCalledWith(expect.arrayContaining([values]))
+  .toHaveBeenCalledWith(expect.objectContaining({ props }))
+  .toHaveBeenCalledWith(expect.stringContaining(string))
+  .toHaveBeenCalledWith(expect.stringMatching(regexp));
+```
+
+### ইন্সটেন্স
+
+```js
+const Fn = jest.fn();
+
+a = new Fn();
+b = new Fn();
+```
+
+```js
+Fn.mock.instances;
+// → [a, b]
+```
+
+
+
+দেখুনঃ [.mock property](http://facebook.github.io/jest/docs/en/mock-functions.html#mock-property)
+
+### কলস
+
+```js
+const fn = jest.fn();
+fn(123);
+fn(456);
+```
+
+```js
+fn.mock.calls.length; // → 2
+fn.mock.calls[0][0]; // → 123
+fn.mock.calls[1][0]; // → 456
+```
+
+
+
+দেখুনঃ [.mock property](http://facebook.github.io/jest/docs/en/mock-functions.html#mock-property)
+
+### রিটার্ন ভ্যালুস
+
+```js
+const fn = jest.fn(() => "hello");
+```
+
+#### অথবা:
+
+```js
+jest.fn().mockReturnValue("hello");
+jest.fn().mockReturnValueOnce("hello");
+```
+
+### মক ইমপ্লিমেনশন
+
+```js
+const fn = jest
+  .fn()
+  .mockImplementationOnce(() => 1)
+  .mockImplementationOnce(() => 2);
+```
+
+
+
+```js
+fn(); // → 1
+fn(); // → 2
+```
+
+## রেফারেন্স
+
+
+
+- <https://devhints.io/jest>
+  
+
+- <http://facebook.github.io/jest/>
+