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.
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) |