How to unit test Java functions with xUnit?

xUnit is a Java unit testing framework that provides concise and powerful assertion and mocking functions to simplify the testing of Java functions. Install xUnit dependencies. Use Assert.assertEquals() to assert. Integrate Mockito for simulation and create mock objects to simulate the behavior of other classes. It is suitable for testing functions that interact with external dependencies. In practice, it can be used to test complex functions, such as functions that calculate factorials.

Use xUnit to unit test Java functions

Introduction

xUnit is Java Commonly used unit testing framework. It provides a concise and powerful set of assertions and mocking features that make testing Java functions easy.

Install xUnit

<dependency>
    <groupId>junit</groupId>
    <artifactId>junit</artifactId>
    <version>4.13.2</version>
    <scope>test</scope>
</dependency>

Use assertions

import org.junit.Assert;

public class CalculatorTest {

    @Test
    public void testAdd() {
        Calculator calculator = new Calculator();
        int result = calculator.add(2, 3);
        // 断言结果应该为 5
        Assert.assertEquals(5, result);
    }
}

Use Mocking

Mockito is a popular mocking library that can be used with xUnit. Mockito allows you to create mock objects that simulate the behavior of other classes or interfaces. This is useful for testing functions that interact with external dependencies.

import org.junit.Before;
import org.junit.Test;
import org.mockito.Mock;
import org.mockito.Mockito;

public class CustomerServiceTest {

    @Mock
    private CustomerRepository customerRepository;

    @Before
    public void setUp() {
        Mockito.when(customerRepository.findById(1)).thenReturn(new Customer("John Doe"));
    }

    @Test
    public void testGetCustomer() {
        CustomerService customerService = new CustomerService(customerRepository);
        Customer customer = customerService.getCustomer(1);
        // 断言获取到的客户名为 "John Doe"
        Assert.assertEquals("John Doe", customer.getName());
    }
}

Practical case

Consider a function that calculates factorial:

public class Factorial {

    public int calculate(int n) {
        if (n == 0) {
            return 1;
        } else {
            return n * calculate(n - 1);
        }
    }
}

Unit test

import org.junit.Assert;

public class FactorialTest {

    @Test
    public void testCalculate() {
        Factorial factorial = new Factorial();
        // 断言 factorial(5) 应为 120
        Assert.assertEquals(120, factorial.calculate(5));
    }
}

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