Writing Unit Test, a simple guide

Testing Pyramid

As a developer in the Digital Factory, you need to write unit tests for every feature (or method) you add, Unit testing is a must in our culture 😉

To help standardize how we write unit tests, here are some basics & good practices through a java example :

A good unit test must be FIRST :

• Fast: The developer shouldn’t hesitate to run the unit tests at any point of their development cycle, They should run and show you the desired output in a matter of seconds
• Independent: For any given unit test, for its environment variables, or its setup. It should be independent of everything else should so that its results are not influenced by any other factor. Generally, tests should follow the pattern: Given, when, then.
• Repeatable: Tests should be repeatable and deterministic, their values shouldn’t change based on being run on different environments
• Self-validating: You shouldn’t need to check manually, whether the test passed or not
• Thorough: T stands for thorough and developers who practice test-driven development also spell it as timely. This means that when testing a function, we should consider a happy path as well as a negative scenario.

A good unit test name should explain a business rule, not a random name 😃

• bad name: shouldCallCreate
• good name: creatingAnomalyWithEmptyDescriptionShouldFail

Sample

package ma.ocpgroup.labs;

import org.springframework.stereotype.Service;

import java.time.LocalDate;
import java.util.Arrays;
import java.util.List;

@Service
public class AnomalyService {
    static List<String> STATUS = Arrays.asList("created", "on-doing", "fixed");


    Anomaly createAnomaly(String description, LocalDate createdAt, String status) throws ConstraintViolationException {
        if (isEmptyString(description)) {
            throw new ConstraintViolationException("Empty description");
        }
        if (createdAt == null) {
            throw new ConstraintViolationException("Empty creation date");
        }
        if (isEmptyString(status)) {
            throw new ConstraintViolationException("Empty status");
        }
        if (!STATUS.contains(status)) {
            throw new ConstraintViolationException("No matching status");
        }
        return new Anomaly(description, createdAt, status);
    }

    boolean isEmptyString(String string) {
        return string == null || string.isEmpty();
    }

}

package ma.ocpgroup.labs;


import org.junit.jupiter.api.Test;

import java.time.LocalDate;

import static org.junit.jupiter.api.Assertions.*;


public class AnomalyServiceTest {

    AnomalyService anomalyService = new AnomalyService();


    @Test
    void creatingWithValidInputsShouldReturnNewAnomaly() throws ConstraintViolationException{
        //given
        String desc = "description de test";
        LocalDate date20210412 = LocalDate.of(2021, 4, 12);
        String statusInput = "created";
        //when
        Anomaly anomaly = anomalyService.createAnomaly(desc, date20210412, statusInput);
        //then
        assertNotNull(anomaly);
        assertEquals(desc, anomaly.getDescription());
        assertEquals(date20210412, anomaly.getCreatedAt());
        assertEquals(statusInput, anomaly.getStatus());
    }



    @Test
    void creatingWithEmptyDescriptionShouldFail(){
        ConstraintViolationException thrown = assertThrows(
                ConstraintViolationException.class,
                () -> anomalyService.createAnomaly(null, LocalDate.now(), "going"),
                "Expected  to throw exception, but it didn't"
        );

        assertTrue(thrown.getMessage().contains("Empty description"));

    }

    @Test
    void creatingWithNullCreationDateShouldFail(){
        ConstraintViolationException thrown = assertThrows(
                ConstraintViolationException.class,
                () -> anomalyService.createAnomaly("description", null, "going"),
                "Expected  to throw exception, but it didn't"
        );

        assertTrue(thrown.getMessage().contains("Empty creation date"));

    }

    @Test
    void creatingWithBadStatusShouldFail(){
        ConstraintViolationException thrown = assertThrows(
                ConstraintViolationException.class,
                () -> anomalyService.createAnomaly("description ", LocalDate.now(), "going"),
                "Expected  to throw exception, but it didn't"
        );

        assertTrue(thrown.getMessage().contains("No matching status"));

    }


}