chapter 02: add a memory calculator in order to test it with state-based testing

Author: devcorpio

chapter_02-a-first-unit-test/MemCalculator/memCalculator.js

@@ -23,6 +23,11 @@ function memCalculator() {
 
         return temp;
     }
+
+    return {
+        add,
+        result,
+    };
 }
 
 module.exports = memCalculator;

chapter_02-a-first-unit-test/MemCalculator/memCalculator.test.js

@@ -0,0 +1,24 @@
+const memCalculator = require('./memCalculator');
+
+let memCalculatorInstance;
+beforeEach(() => {
+    memCalculatorInstance = memCalculator();
+});
+
+describe('result', () => {
+    it('by default returns zero', () => {
+        const lastResult = memCalculatorInstance.result();
+        expect(lastResult).toBe(0);
+    });
+
+    it('changes when call add', () => {
+        const expectedResult = 12;
+
+        memCalculatorInstance.add(5);
+        memCalculatorInstance.add(7);
+
+        const lastResult = memCalculatorInstance.result();
+
+        expect(lastResult).toBe(expectedResult);
+    });
+});