added simple spies example

exercises/05_advanced_testing/03_spies_basic/app.js

@@ -0,0 +1,9 @@
+
+'use strict'
+
+const math = require('./math.js')
+
+module.exports.doAdd = (a, b) => math.add(a, b)
+module.exports.doSubtract = (a, b) => math.subtract(a, b)
+module.exports.doMultiply = (a, b) => math.multiply(a, b)
+module.exports.doDivide = (a, b) => math.divide(a, b)

exercises/05_advanced_testing/03_spies_basic/app.test.js

@@ -0,0 +1,19 @@
+
+'use strict'
+
+const app = require('./app')
+const math = require('./math')
+
+test('calls math.add', () => {
+	const addMock = jest.spyOn(math, 'add')
+
+	// override the implementation
+	addMock.mockImplementation(() => 'mock')
+	expect(app.doAdd(1, 2)).toEqual('mock')
+	expect(addMock).toHaveBeenCalledWith(1, 2)
+
+	// restore the original implementation
+	addMock.mockRestore()
+	expect(app.doAdd(1, 2)).toEqual(3)
+	console.log(addMock.mock.calls)
+})

exercises/05_advanced_testing/03_spies_basic/math.js

@@ -0,0 +1,7 @@
+
+'use strict'
+
+module.exports.add = (a, b) => a + b
+module.exports.subtract = (a, b) => b - a
+module.exports.multiply = (a, b) => a * b
+module.exports.divide = (a, b) => b / a

exercises/05_advanced_testing/03_spies_basic/package.json

@@ -0,0 +1,20 @@
+{
+  "name": "03_spies",
+  "version": "1.0.0",
+  "description": "",
+  "main": "app.js",
+  "scripts": {
+    "test": "./node_modules/.bin/jest",
+    "watch": "./node_modules/.bin/jest --noStackTrace --watchAll"
+  },
+  "author": "",
+  "license": "ISC",
+  "jest": {
+    "testEnvironment": "node",
+    "verbose": true,
+    "collectCoverage": true
+  },
+  "devDependencies": {
+    "jest": "^23.6.0"
+  }
+}