Hamcrest Matchers Exercises

This small exercise is meant to help students get familiar with Hamcrest matchers. The exercise will involve creating a simple class and writing unit tests with Hamcrest to check the properties of that class.

Task: Student Class and Hamcrest Matchers

Step 1: Create a `Student` class

Create a maven project from scratch and add a the dependencies at the bottom of this page to the pom.xml file.

The Student class will have the following properties:

String name
int age
double gpa // Grade Point Average, a number between 0.0 and 4.0
List<Student> friends

It should have:

A constructor to initialize these fields.
Getters for each field.
A method addFriend(Student friend) to add a Student object to the friends list.

import java.util.ArrayList;
import java.util.List;

public class Student {
    private String name;
    private int age;
    private double gpa;
    private List<Student> friends;

    public Student(String name, int age, double gpa) {
        this.name = name;
        this.age = age;
        this.gpa = gpa;
        this.friends = new ArrayList<>();
    }

    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }

    public double getGpa() {
        return gpa;
    }

    public List<Student> getFriends() {
        return friends;
    }

    public void addFriend(Student friend) {
        this.friends.add(friend);
    }
}

Step 2: Write Unit Tests with Hamcrest

Students should write tests using the following Hamcrest matchers:

is // like “name is John”, “age is 24”
equalTo // like age equalTo 24
greaterThan // like gpa greaterThan 3.0
lessThanOrEqualTo // like age lessThanOrEqualTo 25
containsString // like name containsString ‘John’
hasSize // like friends hasSize 3
hasItem // like friends hasItem ‘Alice’ as an object
not // like name not ‘John’
containsInAnyOrder // like friends containsInAnyOrder ‘Alice’, ‘Bob’, ‘Charlie’

Dependencies

To carry out the Hamcrest exercise with JUnit, you will need dependencies for both JUnit and Hamcrest in your pom.xml file if you are using Maven. Below are the necessary dependencies:

1. JUnit Dependency

Since you’re using Java 17, it’s best to use JUnit 5 (Jupiter). JUnit 5 has its own set of dependencies for writing and running tests.

<dependency>
    <groupId>org.junit.jupiter</groupId>
    <artifactId>junit-jupiter-api</artifactId>
    <version>5.9.3</version> <!-- Use the latest version available -->
    <scope>test</scope>
</dependency>
<dependency>
    <groupId>org.junit.jupiter</groupId>
    <artifactId>junit-jupiter-engine</artifactId>
    <version>5.9.3</version>
    <scope>test</scope>
</dependency>

2. Hamcrest Dependency

JUnit 5 doesn’t bundle Hamcrest by default, so you need to include Hamcrest explicitly. Here’s the Maven dependency for Hamcrest:

<dependency>
    <groupId>org.hamcrest</groupId>
    <artifactId>hamcrest</artifactId>
    <version>2.2</version> <!-- Use the latest version available -->
    <scope>test</scope>
</dependency>

How to Run Tests

Make sure that your Maven pom.xml file has the maven-surefire-plugin configured to run JUnit 5 tests:

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-surefire-plugin</artifactId>
            <version>3.0.0-M7</version> <!-- Make sure to use a version that supports JUnit 5 -->
        </plugin>
    </plugins>
</build>

Summary

JUnit 5 for the testing framework.
Hamcrest for matchers.
Maven Surefire Plugin to ensure test cases are executed.