In JUnit 5, we use the assertThrows method to assert that a certain exception is thrown by a method/executable.
We add the following maven dependency to add JUnit 5 to the application:
<dependency><groupId>org.junit.jupiter</groupId><artifactId>junit-jupiter-engine</artifactId><version>5.8.1</version><scope>test</scope></dependency>
The method asserts that the given executable throws an exception of type, expectedType, and returns the exception. This method will fail if the exception thrown is different from the specified exception or if no exception is thrown.
The method optionally takes a string message parameter that is returned as the AssertionFailedError message when the method fails.
public static <T extends Throwable> T assertThrows(Class<T> expectedType, Executable executable)
Class<T> expectedType: This is an expected exception to be thrown by the executable.Executable executable: This is a block of code that throws a Throwable.The method returns the exception thrown by the executable.
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>org.example</groupId>
<artifactId>test</artifactId>
<version>1.0-SNAPSHOT</version>
<properties>
<maven.compiler.source>8</maven.compiler.source>
<maven.compiler.target>8</maven.compiler.target>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>
<dependencies>
<dependency>
<groupId>org.junit.jupiter</groupId>
<artifactId>junit-jupiter-engine</artifactId>
<version>5.8.1</version>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-shade-plugin</artifactId>
<version>2.1</version>
<executions>
<execution>
<phase>package</phase>
<goals>
<goal>shade</goal>
</goals>
<configuration>
<transformers>
<transformer
implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
<mainClass>Main</mainClass>
</transformer>
</transformers>
</configuration>
</execution>
</executions>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.8.1</version>
<configuration>
<source>8</source>
<target>8</target>
</configuration>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-surefire-plugin</artifactId>
<version>2.22.2</version>
</plugin>
</plugins>
</build>
</project>We define a Calculator class that contains an add method that takes two integers and returns their sum. If any integers are null, the method throws a NullPointerException.
In the above code, we concentrate on the CalculatorTest.java file.
messageIfAssertFails that is returned as the AssertionFailedError message if the assertion of the exception thrown fails.add() method with one of the arguments as null throws an exception whose class is Exception. Here, we don’t check the message of the thrown exception.add() method with one of the arguments as null throws an exception whose class is NullPointerException. We also check the message of the thrown exception.Integer.parseInt() throws NumberFormatException while the expected is NullPointerException.