Write junit unit test cases

Junit is a popular Java unit testing framework that helps developers conduct automated unit testing. By using Junit for unit testing, developers can quickly verify the correctness of their code and ensure it behaves as expected under various circumstances. This article will introduce the basic concepts of Junit unit testing and provide several specific code examples.

1. Basic concepts of Junit

Before you start writing Junit tests, you first need to understand several basic concepts.

1.1 Test class

The test class is a Java class that contains multiple test methods. In each test method, we can write corresponding test code to verify the behavior of the code under test.

1.2 Test method

The test method is the method in the test class that actually executes the test. Each test method is marked with the @Test annotation to tell Junit that it is a test method.

1.3 Assertions

Assertions are a key concept used to verify the behavior of code. We can use assertions to determine whether a test passes. If the assertion succeeds, it means the test passed, otherwise it means the test failed.

2. Junit examples

Below we will use several specific examples to demonstrate how to use Junit for unit testing.

2.1 Example 1: Basic usage of test methods

The following is a simple example that demonstrates how to write a test method to verify the behavior of the code under test.

import org.junit.Test;
import static org.junit.Assert.assertEquals;

public class CalculatorTest {
    
    @Test
    public void testAddition() {
        Calculator calculator = new Calculator();
        int result = calculator.add(2, 3);
        assertEquals(5, result);
    }
}

In the above example, we first create an instance of the Calculator class and use the add method to add two numbers. Then use the assertion assertEquals to verify that the results are as expected.

2.2 Example 2: Testing exceptions

Sometimes we need to test the behavior of the code when encountering exceptions. Below is an example that demonstrates how to test that your code throws the correct exception when an exception is encountered.

import org.junit.Test;
import static org.junit.Assert.assertThrows;

public class CalculatorTest {
    
    @Test
    public void testDivisionByZero() {
        Calculator calculator = new Calculator();
        assertThrows(ArithmeticException.class, () -> {
            calculator.divide(10, 0);
        });
    }
}

In the above example, we use assertThrows assertion to verify whether the code will throw ArithmeticException when dividing by 0.

3. Run Junit tests

After writing the Junit test code, we need to use Junit to run these tests. Today's Java development environments usually integrate support for Junit. We only need to select the test class to run and click the "Run" button.

After all the tests have been run, we can see the running results of each test, as well as the number of passed and failed tests.

Summary

Junit is a popular Java unit testing framework that can help developers conduct automated unit testing by using Junit. This article introduces the basic concepts of Junit and provides several concrete code examples. I hope these examples can help readers better understand and use Junit for unit testing.

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