Unit Testing

Unit tests are deterministic tests that exercise a discrete unit of the application, such as a function, method, or UI component, in isolation to determine whether it behaves as expected.

Testing Glossary

When testing the specs of functions, prefer testing public API (methods, interfaces, functions) to private API: the spec of private functions and methods are meant to change easily in the future, and unit-testing them would amount to writing a Change Detector Test, which is an anti-pattern.

The purpose of unit tests are to:

  • Verify the functionality of a unit (method, class, function, etc.) in isolation
  • Good for testing hi-complexity logic where there may be many permutations (e.g. business logic)
  • Keep Cyclomatic Complexity low through good separations of concerns and architecture


  • Unit tests are low-level and focus on discrete units of the application
  • All dependencies are typically replaced with test-doubles to remove non-determinism
  • Unit tests are fast to execute
  • Test Suite is ran after every code change
  • Run a subset of your test suite based on the part of the code your are currently working on
    • Following TDD practices plus the watch functionality of certain testing frameworks is an easy way to achieve this
  • Pre-commit hooks to run the test suite before committing code to version control
    • Verification during PR and during the CI build on the HEAD to verify that earlier verification happened and was effective.
  • Discourage disabling of static tests (e.g. skipping tests, ignoring warnings, ignoring code on coverage evaluation, etc)
  • Write custom rules (lint, formatting, etc) for common code review feedback



    // Example from lodash
    describe('castArray', () => {
        it('should wrap non-array items in an array', () => {
            const values = falsey.concat(true, 1, 'a', { a: 1 });
            const expected = lodashStable.map(values, (value) => [value]);
            const actual = lodashStable.map(values, castArray);


        it('should return array values by reference', () => {
            const array = [1];

        it('should return an empty array when no arguments are given', () => {
    // Mock the userService
    public void verifyMockedUserDetails() throws Exception {

      // ===============Arrange===============
      ObjectMapper mapper = new ObjectMapper();
      User userMockData = mapper.readValue(new File(TestConstants.DATA_FILE_ROOT + "user_mock.json"), User.class);

      // This code mocks the getUserInfo method for userService
      // Any call made to the getUserInfo will not make actual method call instead
      // returns the userMockData

      // ===============Act===============
      RequestBuilder requestBuilder = MockMvcRequestBuilders.get("/user/" + TestConstants.userId)

      MvcResult mvcResponse = mockMvc.perform(requestBuilder).andReturn();
      String responsePayload = mvcResponse.getResponse().getContentAsString();
      String status = JsonPath.parse(responsePayload).read("$.STATUS");
        Map<String, String> userMap = JsonPath.parse(responsePayload).read("$.payload");

      // ===============Assert===============
      JSONAssert.assertEquals(TestConstants.PARTIAL_MOCK_SUCCESS_PAYLOAD, responsePayload, false); // disable strict
      // validate the expected userMockData is matching with actual userMap Data
      Assert.assertEquals(TestConstants.SUCCESS, status);
      Assert.assertEquals(userMockData.getManager(), userMap.get("manager"));
      Assert.assertEquals(userMockData.getVp(), userMap.get("vp"));
      Assert.assertEquals(userMockData.getOrganization(), userMap.get("organization"));
      Assert.assertEquals(userMockData.getDirector(), userMap.get("director"));
      Assert.assertEquals(userMockData.getCostcenter(), userMap.get("costcenter"));
Platform Tools
Android Framework: JUnit5
Assertion: Google Truth
iOS XCTest
Web Framework: jest
Assertion & Mocking: expect (jest), jest-dom, others as necessary
Code Coverage: instanbul/nyc (jest)
Java BE Framework: TestNG, JUnit5
Code Coverage: sonar (sonarlint)
Mocking: Powermock, Mockitoi
Assertion: REST Assured, Truth, TestNG/JUnit5
JS/node BE Framework: jest
Assertion & Mocking: expect (jest) - generic, supertest or nock - http server endpoint, apollo - graphql server testing
Code Coverage: instanbul/nyc (jest)
Last modified December 15, 2023: Reorganize (7579932)