Chapter 8: add first recipe samples

Chapter08/testing-with-tape/calculator.js

@@ -0,0 +1,15 @@
+module.exports.add = (number1, number2) => {
+  return number1 + number2;
+};
+
+module.exports.subtract = (number1, number2) => {
+  return number1 - number2;
+};
+
+module.exports.multiply = (number1, number2) => {
+  return number1 * number2;
+};
+
+module.exports.divide = (number1, number2) => {
+  return number1 / number2;
+};