tests: implement basic jest tests

src/01-simple-tests/index.test.ts

@@ -1,32 +1,67 @@
 // Uncomment the code below and write your tests
-// import { simpleCalculator, Action } from './index';
+import { simpleCalculator, Action } from './index';
 
 describe('simpleCalculator tests', () => {
   test('should add two numbers', () => {
-    // Write your test here
+    expect(simpleCalculator({ a: 2, b: 3, action: Action.Add })).toBe(5);
+    expect(simpleCalculator({ a: -2, b: -3, action: Action.Add })).toBe(-5);
+    expect(simpleCalculator({ a: -5, b: 3, action: Action.Add })).toBe(-2);
   });
 
   test('should subtract two numbers', () => {
-    // Write your test here
+    expect(simpleCalculator({ a: 2, b: 3, action: Action.Subtract })).toBe(-1);
+    expect(simpleCalculator({ a: -2, b: -3, action: Action.Subtract })).toBe(1);
+    expect(simpleCalculator({ a: 5, b: 3, action: Action.Subtract })).toBe(2);
   });
 
   test('should multiply two numbers', () => {
-    // Write your test here
+    expect(simpleCalculator({ a: 2, b: 3, action: Action.Multiply })).toBe(6);
+    expect(simpleCalculator({ a: -2, b: -3, action: Action.Multiply })).toBe(6);
+    expect(simpleCalculator({ a: -2, b: 3, action: Action.Multiply })).toBe(-6);
+    expect(simpleCalculator({ a: -2, b: 0, action: Action.Multiply })).toBe(-0);
   });
 
   test('should divide two numbers', () => {
-    // Write your test here
+    expect(simpleCalculator({ a: 6, b: 2, action: Action.Divide })).toBe(3);
+    expect(simpleCalculator({ a: -6, b: 2, action: Action.Divide })).toBe(-3);
+    expect(simpleCalculator({ a: -6, b: -2, action: Action.Divide })).toBe(3);
+    expect(simpleCalculator({ a: -6, b: 0, action: Action.Divide })).toBe(
+      Number.NEGATIVE_INFINITY,
+    );
+    expect(simpleCalculator({ a: 6, b: 4, action: Action.Divide })).toBe(1.5);
   });
 
   test('should exponentiate two numbers', () => {
-    // Write your test here
+    expect(simpleCalculator({ a: 2, b: 2, action: Action.Exponentiate })).toBe(
+      4,
+    );
+    expect(simpleCalculator({ a: -2, b: 2, action: Action.Exponentiate })).toBe(
+      4,
+    );
+    expect(simpleCalculator({ a: -2, b: 3, action: Action.Exponentiate })).toBe(
+      -8,
+    );
+    expect(simpleCalculator({ a: 6, b: 0, action: Action.Exponentiate })).toBe(
+      1,
+    );
+    expect(simpleCalculator({ a: -6, b: 0, action: Action.Exponentiate })).toBe(
+      1,
+    );
+    expect(
+      simpleCalculator({ a: 9, b: 0.5, action: Action.Exponentiate }),
+    ).toBe(3);
+    expect(simpleCalculator({ a: 2, b: -1, action: Action.Exponentiate })).toBe(
+      0.5,
+    );
   });
 
   test('should return null for invalid action', () => {
-    // Write your test here
+    expect(simpleCalculator({ a: 6, b: 0, action: 'lg' })).toBe(null);
+    expect(simpleCalculator({ a: 6, b: 0, action: 5 })).toBe(null);
   });
 
   test('should return null for invalid arguments', () => {
-    // Write your test here
+    expect(simpleCalculator({ a: '6', b: 2, action: Action.Add })).toBe(null);
+    expect(simpleCalculator({ a: 6, b: '2', action: Action.Add })).toBe(null);
   });
 });

src/02-table-tests/index.test.ts

@@ -1,17 +1,21 @@
-// Uncomment the code below and write your tests
-/* import {  simpleCalculator, Action } from './index';
+import { simpleCalculator, Action } from './index';
 
 const testCases = [
-    { a: 1, b: 2, action: Action.Add, expected: 3 },
-    { a: 2, b: 2, action: Action.Add, expected: 4 },
-    { a: 3, b: 2, action: Action.Add, expected: 5 },
-    // continue cases for other actions    
-]; */
+  { a: 1, b: 2, action: Action.Add, expected: 3 },
+  { a: 2, b: 2, action: Action.Add, expected: 4 },
+  { a: 3, b: 2, action: Action.Add, expected: 5 },
+  { a: 3, b: 2, action: Action.Subtract, expected: 1 },
+  { a: -3, b: -2, action: Action.Subtract, expected: -1 },
+  { a: 3, b: 2, action: Action.Multiply, expected: 6 },
+  { a: 3, b: 2, action: Action.Divide, expected: 1.5 },
+  { a: 3, b: 2, action: Action.Exponentiate, expected: 9 },
+];
 
 describe('simpleCalculator', () => {
-  // This test case is just to run this test suite, remove it when you write your own tests
-  test('should blah-blah', () => {
-    expect(true).toBe(true);
-  });
-  // Consider to use Jest table tests API to test all cases above
+  test.each(testCases)(
+    'test $action with $a, $b arguments',
+    ({ a, b, expected, action }) => {
+      expect(simpleCalculator({ a, b, action })).toBe(expected);
+    },
+  );
 });

src/03-error-handling-async/index.test.ts

@@ -1,30 +1,37 @@
-// Uncomment the code below and write your tests
-// import { throwError, throwCustomError, resolveValue, MyAwesomeError, rejectCustomError } from './index';
+import {
+  throwError,
+  throwCustomError,
+  resolveValue,
+  MyAwesomeError,
+  rejectCustomError,
+} from './index';
 
 describe('resolveValue', () => {
   test('should resolve provided value', async () => {
-    // Write your test here
+    await expect(resolveValue('resolved value')).resolves.toBe(
+      'resolved value',
+    );
   });
 });
 
 describe('throwError', () => {
   test('should throw error with provided message', () => {
-    // Write your test here
+    expect(() => throwError('test message')).toThrowError('test message');
   });
 
   test('should throw error with default message if message is not provided', () => {
-    // Write your test here
+    expect(throwError).toThrowError('Oops!');
   });
 });
 
 describe('throwCustomError', () => {
   test('should throw custom error', () => {
-    // Write your test here
+    expect(throwCustomError).toThrowError(MyAwesomeError);
   });
 });
 
 describe('rejectCustomError', () => {
   test('should reject custom error', async () => {
-    // Write your test here
+    expect(rejectCustomError).rejects.toThrowError(MyAwesomeError);
   });
 });

src/04-test-class/index.test.ts

@@ -1,44 +1,91 @@
-// Uncomment the code below and write your tests
-// import { getBankAccount } from '.';
+import {
+  getBankAccount,
+  InsufficientFundsError,
+  SynchronizationFailedError,
+  TransferFailedError,
+} from '.';
+import lodash from 'lodash';
 
 describe('BankAccount', () => {
+  const initialBalance = 1000;
+  let bankAccount = getBankAccount(initialBalance);
+  let destinationAccount = getBankAccount(initialBalance);
+
+  beforeAll(() => {
+    bankAccount = getBankAccount(initialBalance);
+    destinationAccount = getBankAccount(initialBalance);
+  });
+
   test('should create account with initial balance', () => {
-    // Write your test here
+    expect(bankAccount.getBalance()).toBe(initialBalance);
   });
 
   test('should throw InsufficientFundsError error when withdrawing more than balance', () => {
-    // Write your test here
+    expect(() => bankAccount.withdraw(initialBalance + 1000)).toThrowError(
+      InsufficientFundsError,
+    );
   });
 
   test('should throw error when transferring more than balance', () => {
-    // Write your test here
+    expect(() =>
+      bankAccount.transfer(initialBalance + 1000, destinationAccount),
+    ).toThrowError(InsufficientFundsError);
   });
 
   test('should throw error when transferring to the same account', () => {
-    // Write your test here
+    expect(() =>
+      bankAccount.transfer(initialBalance - 500, bankAccount),
+    ).toThrowError(TransferFailedError);
   });
 
   test('should deposit money', () => {
-    // Write your test here
+    const deposit = 500;
+    const currentBalance = bankAccount.getBalance();
+    expect(bankAccount.deposit(deposit).getBalance()).toBe(
+      currentBalance + deposit,
+    );
   });
 
   test('should withdraw money', () => {
-    // Write your test here
+    const withdraw = 200;
+    const currentBalance = bankAccount.getBalance();
+    expect(bankAccount.withdraw(withdraw).getBalance()).toBe(
+      currentBalance - withdraw,
+    );
   });
 
   test('should transfer money', () => {
-    // Write your test here
+    const transfer = 200;
+    const currentBalance = bankAccount.getBalance();
+    expect(
+      bankAccount.transfer(transfer, destinationAccount).getBalance(),
+    ).toBe(currentBalance - transfer);
+
+    expect(destinationAccount.getBalance()).toBe(initialBalance + transfer);
   });
 
   test('fetchBalance should return number in case if request did not failed', async () => {
-    // Write your tests here
+    const mockedValue = 400;
+    jest.spyOn(lodash, 'random').mockReturnValue(mockedValue);
+
+    const result = await bankAccount.fetchBalance();
+    expect(result).toBe(mockedValue);
   });
 
   test('should set new balance if fetchBalance returned number', async () => {
-    // Write your tests here
+    const mockedValue = 400;
+    jest.spyOn(lodash, 'random').mockReturnValue(mockedValue);
+
+    await bankAccount.synchronizeBalance();
+    expect(bankAccount.getBalance()).toBe(mockedValue);
   });
 
   test('should throw SynchronizationFailedError if fetchBalance returned null', async () => {
-    // Write your tests here
+    const mockedValue = 0;
+    jest.spyOn(lodash, 'random').mockReturnValue(mockedValue);
+
+    expect(bankAccount.synchronizeBalance()).rejects.toThrowError(
+      SynchronizationFailedError,
+    );
   });
 });

src/05-partial-mocking/index.test.ts

@@ -1,8 +1,15 @@
-// Uncomment the code below and write your tests
-// import { mockOne, mockTwo, mockThree, unmockedFunction } from './index';
+import { mockOne, mockTwo, mockThree, unmockedFunction } from './index';
 
 jest.mock('./index', () => {
-  // const originalModule = jest.requireActual<typeof import('./index')>('./index');
+  const originalModule =
+    jest.requireActual<typeof import('./index')>('./index');
+  return {
+    __esModule: true,
+    ...originalModule,
+    mockOne: jest.fn(),
+    mockTwo: jest.fn(),
+    mockThree: jest.fn(),
+  };
 });
 
 describe('partial mocking', () => {
@@ -11,10 +18,17 @@ describe('partial mocking', () => {
   });
 
   test('mockOne, mockTwo, mockThree should not log into console', () => {
-    // Write your test here
+    const log = jest.spyOn(console, 'log');
+    mockOne();
+    mockTwo();
+    mockThree();
+
+    expect(log).not.toBeCalled();
   });
 
   test('unmockedFunction should log into console', () => {
-    // Write your test here
+    const log = jest.spyOn(console, 'log');
+    unmockedFunction();
+    expect(log).toHaveBeenCalled();
   });
 });

src/06-mocking-node-api/index.test.ts

@@ -1,5 +1,11 @@
 // Uncomment the code below and write your tests
-// import { readFileAsynchronously, doStuffByTimeout, doStuffByInterval } from '.';
+import { doStuffByInterval, doStuffByTimeout, readFileAsynchronously } from '.';
+import path from 'path';
+import fs from 'fs';
+import fsPromises from 'fs/promises';
+
+jest.mock('fs');
+jest.mock('fs/promises');
 
 describe('doStuffByTimeout', () => {
   beforeAll(() => {
@@ -11,11 +17,18 @@ describe('doStuffByTimeout', () => {
   });
 
   test('should set timeout with provided callback and timeout', () => {
-    // Write your test here
+    jest.spyOn(global, 'setTimeout');
+    const cb = jest.fn();
+    doStuffByTimeout(cb, 1000);
+    expect(setTimeout).toBeCalledWith(cb, 1000);
   });
 
   test('should call callback only after timeout', () => {
-    // Write your test here
+    const cb = jest.fn();
+    doStuffByTimeout(cb, 1000);
+    expect(cb).not.toBeCalled();
+    jest.advanceTimersByTime(1000);
+    expect(cb).toBeCalled();
   });
 });
 
@@ -29,24 +42,44 @@ describe('doStuffByInterval', () => {
   });
 
   test('should set interval with provided callback and timeout', () => {
-    // Write your test here
+    jest.spyOn(global, 'setInterval');
+    const cb = jest.fn();
+    doStuffByInterval(cb, 1000);
+    expect(setInterval).toBeCalledWith(cb, 1000);
   });
 
   test('should call callback multiple times after multiple intervals', () => {
-    // Write your test here
+    const cb = jest.fn();
+    doStuffByInterval(cb, 1000);
+    expect(cb).not.toBeCalled();
+    jest.advanceTimersByTime(1000);
+    expect(cb).toBeCalledTimes(1);
+    jest.advanceTimersByTime(2000);
+    expect(cb).toBeCalledTimes(3);
   });
 });
 
 describe('readFileAsynchronously', () => {
   test('should call join with pathToFile', async () => {
-    // Write your test here
+    const join = jest.spyOn(path, 'join');
+    const pathToFile = 'test.txt';
+    readFileAsynchronously(pathToFile);
+    expect(join).toHaveBeenCalledWith(expect.anything(), pathToFile);
   });
 
   test('should return null if file does not exist', async () => {
-    // Write your test here
+    jest.spyOn(fs, 'existsSync').mockReturnValue(false);
+    const pathToFile = 'fake-path.txt';
+
+    await expect(readFileAsynchronously(pathToFile)).resolves.toBeNull();
   });
 
   test('should return file content if file exists', async () => {
-    // Write your test here
+    const fileContent = 'File content';
+    jest.spyOn(fs, 'existsSync').mockReturnValue(true);
+    jest.spyOn(fsPromises, 'readFile').mockResolvedValue(fileContent);
+    const pathToFile = 'fake-path.txt';
+
+    await expect(readFileAsynchronously(pathToFile)).resolves.toBe(fileContent);
   });
 });