Make unit test with jest liabrary

.gitignore

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+node_modules/

calculator.js

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+module.exports = class calculator {
+ add(num1, num2) { 
+  return num1 + num2;
+ }
+  subtract(num1, num2) {
+      return num1 - num2;
+ }
+  divide(num1, num2) {
+    if (num2 === 0) {
+      return undefined;
+    } else {
+      return num1 / num2;
+    }
+   }
+  multiply(num1, num2) {
+    return num1 * num2;
+   }
+}

calculator.test.js

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+const Calculator = require('./calculator');
+
+const calc = new Calculator();
+
+describe('addition', () => {
+  test('Add numbers', () => {
+    expect(calc.add(2, 3)).toBe(5);
+    expect(calc.add(10, 20)).toBe(30);
+    expect(calc.add(-10, 5)).toBe(-5);
+  });
+});
+
+describe('substraction', () => {
+  test('subtract numbers', () => {
+    expect(calc.subtract(2, 3)).toBe(-1);
+    expect(calc.subtract(20, 10)).toBe(10);
+    expect(calc.subtract(-10, 5)).toBe(-15);
+  });
+});
+
+describe('division', () => {
+  test('division of numbers', () => {
+    expect(calc.divide(2, 0)).toBeUndefined();
+    expect(calc.divide(10, 20)).toBe(0.5);
+    expect(calc.divide(-10, 5)).toBe(-2);
+  });
+});
+
+describe('multiolication', () => {
+  test('Multiply numbers', () => {
+    expect(calc.multiply(2, 3)).toBe(6);
+    expect(calc.multiply(10, 20)).toBe(200);
+    expect(calc.multiply(0, 5)).toBe(0);
+  });
+});

capital.js

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+module.exports = function capitalize(str) {
+  return str.charAt(0).toUpperCase() + str.slice(1).toLowerCase();
+}

capital.test.js

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+const capitalize = require('./capital');
+
+test('Capitalize First Letter', () => {
+  expect(capitalize('pakistan')).toBe('Pakistan');
+  expect(capitalize('multan')).toBe('Multan');
+  expect(capitalize('tahseen')).toBe('Tahseen');
+});