added small exercise for jest testing

step2-04/README.md

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+# Step 2.4
+
+Testing Typescript code with jest.
+
+# Exercise
+
+1. copy the generic `Stack<T>` code you have developed in Step 2.1
+
+2. import the `Stack<T>` class into `stack.spec.ts`
+
+3. Follow the instructions inside the file to complete the two tests

step2-04/demo/src/index.spec.ts

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+import { square } from '.';
+
+describe('jest example', () => {
+  beforeEach(() => {
+    jest.resetModules();
+  });
+
+  it('should be able to give the square of two numbers', () => {
+    console.log('test');
+    expect(square(5)).toBe(25);
+  });
+
+  it('should increment counter', () => {
+    const { increment } = require('.');
+    expect(increment()).toBe(1);
+  });
+
+  it('should decrement counter', () => {
+    const { decrement } = require('.');
+    expect(decrement()).toBe(-1);
+  });
+
+  it('should retrieve count', () => {
+    const { decrement, getCount, increment } = require('.');
+    increment();
+    increment();
+    decrement();
+    increment();
+
+    expect(getCount()).toBe(2);
+  });
+});

step2-04/demo/src/index.ts

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+let counter = 0;
+
+export function getCount() {
+  return counter;
+}
+
+export function increment() {
+  return ++counter;
+}
+
+export function decrement() {
+  return --counter;
+}
+
+export function square(x: number) {
+  return x * x;
+}

step2-04/demo/src/store/index.ts

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+export type FilterTypes = 'all' | 'active' | 'completed';
+
+export interface TodoItem {
+  label: string;
+  completed: boolean;
+}
+
+export interface Store {
+  todos: {
+    [id: string]: TodoItem;
+  };
+
+  filter: FilterTypes;
+}

step2-04/exercise/src/stack.spec.ts

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+describe('stack', () => {
+  it('should push item to the top of the stack', () => {
+    // implement test here:
+    // 1. require the stack
+    // 2. create stack push calls to place some items in the stack
+    // 3. write assertions via the expect() API
+  });
+
+  it('should pop the item from the top of stack', () => {
+    // implement test here:
+    // 1. require the stack
+    // 2. create stack push calls to place some items in the stack
+    // 3. pop a few items off the stack
+    // 4. write assertions via the expect() API
+  });
+});

step2-04/exercise/src/stack.ts

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+// Place your implementation from Step 2-01 exercise here

step2-04/index.spec.ts

@@ -1,16 +0,0 @@
-import { square } from '.';
-
-describe('square', () => {
-  beforeEach(() => {
-    console.log('this happens before each test');
-  });
-
-  afterEach(() => {
-    console.log('this happens after each test');
-  });
-
-  it('should be able to give the square of two numbers', () => {
-    console.log('test');
-    expect(square(5)).toBe(25);
-  });
-});

step2-04/index.ts

@@ -1,3 +0,0 @@
-export function square(x: number) {
-  return x * x;
-}