First commit

.gitignore

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+node_modules
+coverage

app.js

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+const express = require('express');
+const app = express();
+
+const { add, subtract } = require('./calculator');
+
+app.get('/add', (req, res) => {
+  let { value1, value2 } = req.query;
+  value1 = parseInt(value1);
+  value2 = parseInt(value2);
+  res.json({
+    result: add(value1, value2),
+  });
+});
+
+app.get('/subtract', (req, res) => {
+  let { value1, value2 } = req.query;
+  value1 = parseInt(value1);
+  value2 = parseInt(value2);
+  res.json({
+    result: subtract(value1, value2),
+  });
+});
+
+module.exports = app;

app.test.js

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+const app = require('./app');
+const supertest = require('supertest');
+const request = supertest(app); //arrange
+
+test('gets the add endpoint', async done => {
+  const response = await request.get('/add?value1=2&value2=2'); //Act
+  expect(response.status).toBe(200);
+  expect(response.type).toBe('application/json');
+  expect(response.body.result).toBe(4);
+  done();
+});
+
+test('gets the subtract endpoint', async done => {
+  const response = await request.get('/subtract?value1=2&value2=4'); //Act
+  expect(response.status).toBe(200);
+  expect(response.type).toBe('application/json');
+  expect(response.body.result).not.toBeNull();
+  expect(response.body.result).toBe(-2);
+  done();
+});

calculator.js

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+function add(a, b) {
+  return a + b;
+}
+
+function subtract(a, b) {
+  return a - b;
+}
+
+module.exports = { add, subtract };

calculator.test.js

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+const { add, subtract } = require('./calculator'); //Arrange
+
+describe('add operation', () => {
+  test('adds 1 + 2 to equal 3', () => {
+    var value = add(1, 2); //Act
+    expect(value).toBe(3); //Assert
+  });
+
+  test('adds 5 + 5 to equal 10', () => {
+    var value = add(5, 5); //Act
+    expect(value).toBe(10); //Assert
+  });
+});
+
+describe('subtract operation', () => {
+  test('subtracts 5 - 5 to equal 0', () => {
+    var value = subtract(5, 5); //Act
+    expect(value).toBe(0); //Assert
+  });
+
+  test('subtracts 3 - 2 to equal 1', () => {
+    var value = subtract(3, 2); //Act
+    expect(value).toBe(1); //Assert
+  });
+});