Unit Testing

3 minute read

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

Principles

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

Recommended Best Practices

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

Resources

Examples

    // 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);

            expect(actual).toEqual(expected);
        });

        it('should return array values by reference', () => {
            const array = [1];
            expect(castArray(array)).toBe(array);
        });

        it('should return an empty array when no arguments are given', () => {
            expect(castArray()).toEqual([]);
        });
    });

    @Test
    // 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
      Mockito.when(userService.getUserInfo(TestConstants.userId)).thenReturn(userMockData);

      // ===============Act===============
      RequestBuilder requestBuilder = MockMvcRequestBuilders.get("/user/" + TestConstants.userId)
      .accept(MediaType.APPLICATION_JSON);

      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"));
    }

Recommended Tooling

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)