How to use methods in Java test class

How to use methods in Java test classes

In Java, test classes are an important tool for testing the functionality and correctness of methods. Test classes can use a variety of different methods to test various aspects of a method. Some common testing methods will be introduced below and specific code examples will be given.

1. Unit testing

Unit testing is one of the most common testing methods. It is used to test the smallest unit of a method - that is, a part of the method or a function.

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

public class CalculatorTest {
    
    @Test
    public void testAdd() {
        Calculator calculator = new Calculator();
        int result = calculator.add(3, 5);
        assertEquals(8, result);
    }
}

In the above code, we used the JUnit framework for testing. A CalculatorTest class is defined, and a test method testAdd is marked in it using the @Test annotation. In the test method, we created a Calculator object, called the add method, and used the assertEquals method to assert whether the actual result is the expected result. consistent.

2. Parameterized testing

Parameterized testing allows us to use different parameters to test a method to cover different situations.

import org.junit.Test;
import org.junit.runner.RunWith;
import org.junit.runners.Parameterized;
import java.util.Arrays;
import java.util.Collection;

@RunWith(Parameterized.class)
public class CalculatorTest {
    private int a;
    private int b;
    private int expected;
    
    public CalculatorTest(int a, int b, int expected) {
        this.a = a;
        this.b = b;
        this.expected = expected;
    }
    
    @Parameterized.Parameters
    public static Collection<Object[]> data() {
        return Arrays.asList(new Object[][] {
            {1, 2, 3},
            {4, 5, 9},
            {6, 7, 13}
        });
    }
    
    @Test
    public void testAdd() {
        Calculator calculator = new Calculator();
        int result = calculator.add(a, b);
        assertEquals(expected, result);
    }
}

In the above code, we use JUnit's parameterized testing function. Use the @RunWith(Parameterized.class) annotation to specify a parameterized test runner. Three private variables a, b and expected are defined in the test class, and these variables are initialized through the constructor. Use the @Parameterized.Parameters annotation to specify the test data, and use the Arrays.asList method to convert the test data to a Collection. In the test method, we also create a Calculator object, call the add method, and then use the assertEquals method to assert whether the actual result is the expected result. consistent.

3. Exception testing

Exception testing is used to test whether a method will throw an exception under specific circumstances.

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

public class CalculatorTest {
    
    @Test(expected = ArithmeticException.class)
    public void testDivideByZero() {
        Calculator calculator = new Calculator();
        calculator.divide(6, 0);
    }
}

In the above code, we use the @Test(expected = ArithmeticException.class) annotation to predict the divide in Calculator The method will throw an ArithmeticException exception. In the test method, we create a Calculator object and call the divide method. Since the divisor is 0, an exception will be thrown. Since we specified the predicted exception type, the test will succeed.

Summary:

Through unit testing, parameterized testing, exception testing and other methods, we can more comprehensively test the function and correctness of a method. Test class is one of the essential tools in Java development, which can help us ensure the quality and reliability of the code. I hope the above code example will help you understand how Java test classes use methods.

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