Test Interfaces and Default Methods in JUnit 5

JUnit Jupiter allows @Test, @RepeatedTest, @ParameterizedTest, @TestFactory, @TestTemplate, @BeforeEach, and @AfterEach to be declared on interface default methods.

@BeforeAll and @AfterAll can either be declared on static methods in a test interface or on interface default methods if the test interface or test class is annotated with @TestInstance(Lifecycle.PER_CLASS)

@ExtendWith and @Tag can be declared on a test interface so that classes that implement the interface automatically inherit its tags and extensions.

Finally, In your test class, you can implement these test interfaces to have them applied.

Let’s try to understand the above concept using a demo project:

pom.xml

<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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<groupId>com.kkjavatutorials</groupId>
	<artifactId>JUnit5TestInterfacesAndDefaultMethodsExample</artifactId>
	<version>0.0.1-SNAPSHOT</version>

	<properties>
		<maven.compiler.target>8</maven.compiler.target>
		<maven.compiler.source>8</maven.compiler.source>
		<junit.jupiter.version>5.6.2</junit.jupiter.version>
	</properties>

	<dependencies>

		<dependency>
			<groupId>org.junit.jupiter</groupId>
			<artifactId>junit-jupiter-api</artifactId>
			<version>${junit.jupiter.version}</version>
			<scope>test</scope>
		</dependency>

		<dependency>
			<groupId>org.junit.jupiter</groupId>
			<artifactId>junit-jupiter-engine</artifactId>
			<version>${junit.jupiter.version}</version>
			<scope>test</scope>
		</dependency>

	</dependencies>
</project>

<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 https://maven.apache.org/xsd/maven-4.0.0.xsd">

<groupId>com.kkjavatutorials</groupId>

<artifactId>JUnit5TestInterfacesAndDefaultMethodsExample</artifactId>

<version>0.0.1-SNAPSHOT</version>

<maven.compiler.target>8</maven.compiler.target>

<maven.compiler.source>8</maven.compiler.source>

<junit.jupiter.version>5.6.2</junit.jupiter.version>

</properties>

<groupId>org.junit.jupiter</groupId>

<artifactId>junit-jupiter-api</artifactId>

<version>${junit.jupiter.version}</version>

</dependency>

<groupId>org.junit.jupiter</groupId>

<artifactId>junit-jupiter-engine</artifactId>

<version>${junit.jupiter.version}</version>

</dependency>

</dependencies>

</project>

LifecycleLoggerTest.java

package com.kkjavatutorials;

import java.util.logging.Logger;

import org.junit.jupiter.api.AfterAll;
import org.junit.jupiter.api.AfterEach;
import org.junit.jupiter.api.BeforeAll;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.TestInfo;
import org.junit.jupiter.api.TestInstance;
import org.junit.jupiter.api.TestInstance.Lifecycle;

@TestInstance(value = Lifecycle.PER_CLASS)
public interface LifecycleLoggerTest {

    static final Logger LOG = Logger.getLogger(LifecycleLoggerTest.class.getName());

    @BeforeAll
    default void beforeAll() {
        LOG.info("This Method runs before all tests");
    }

    @AfterAll
    default void afterAll() {
        LOG.info("This Method runs after all tests");
    }

    @BeforeEach
    default void beforeEach(TestInfo testInfo) {
        LOG.info(() -> String.format("About to execute [%s]",
            testInfo.getDisplayName()));
    }

    @AfterEach
    default void afterEach(TestInfo testInfo) {
        LOG.info(() -> String.format("Finished executing [%s]",
            testInfo.getDisplayName()));
    }
}

package com.kkjavatutorials;

import java.util.logging.Logger;

import org.junit.jupiter.api.AfterAll;

import org.junit.jupiter.api.AfterEach;

import org.junit.jupiter.api.BeforeAll;

import org.junit.jupiter.api.BeforeEach;

import org.junit.jupiter.api.TestInfo;

import org.junit.jupiter.api.TestInstance;

import org.junit.jupiter.api.TestInstance.Lifecycle;

@TestInstance(value = Lifecycle.PER_CLASS)

public interface LifecycleLoggerTest {

static final Logger LOG = Logger.getLogger(LifecycleLoggerTest.class.getName());

@BeforeAll

default void beforeAll() {

LOG.info("This Method runs before all tests");

}

@AfterAll

default void afterAll() {

LOG.info("This Method runs after all tests");

}

@BeforeEach

default void beforeEach(TestInfo testInfo) {

LOG.info(() -> String.format("About to execute [%s]",

testInfo.getDisplayName()));

}

@AfterEach

default void afterEach(TestInfo testInfo) {

LOG.info(() -> String.format("Finished executing [%s]",

testInfo.getDisplayName()));

}

InterfaceDynamicTestsDemo.java

package com.kkjavatutorials;

import static org.junit.jupiter.api.Assertions.assertTrue;
import static org.junit.jupiter.api.DynamicTest.dynamicTest;

import java.util.stream.Stream;

import org.junit.jupiter.api.DynamicTest;
import org.junit.jupiter.api.TestFactory;

public interface InterfaceDynamicTestsDemo {

    @TestFactory
    default Stream<DynamicTest> dynamicTestsForPalindromes() {
        return Stream.of("pop", "radar", "mom", "dad","madam")
            .map(inputText -> dynamicTest(inputText, () -> assertTrue(isPalindrome(inputText))));
    }

    /**
     * Method to check whether input String is Palindrome or not
     * @param inputText 
     * @return return true if input is Palindrome else false
     */
    default boolean isPalindrome(String inputText) {
		return new StringBuffer(inputText).reverse().toString().equals(inputText);
    }
}

package com.kkjavatutorials;

import static org.junit.jupiter.api.Assertions.assertTrue;

import static org.junit.jupiter.api.DynamicTest.dynamicTest;

import java.util.stream.Stream;

import org.junit.jupiter.api.DynamicTest;

import org.junit.jupiter.api.TestFactory;

public interface InterfaceDynamicTestsDemo {

@TestFactory

default Stream<DynamicTest> dynamicTestsForPalindromes() {

return Stream.of("pop", "radar", "mom", "dad","madam")

.map(inputText -> dynamicTest(inputText, () -> assertTrue(isPalindrome(inputText))));

}

/**

* Method to check whether input String is Palindrome or not

* @param inputText

* @return return true if input is Palindrome else false

default boolean isPalindrome(String inputText) {

return new StringBuffer(inputText).reverse().toString().equals(inputText);

}

The output of the above project:

You May Also Like:

Junit 5 Architecture
JUnit 5 Annotations
JUnit 5 Maven Dependency
JUnit 5 with Gradle Dependency
JUnit 5 Test Lifecycle
JUnit 5 @BeforeAll annotation example
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JUnit 5 @BeforeEach and @AfterEach annotation Example
JUnit 5 Display Names
Assertions in JUnit 5 Examples
Third-party Assertion Libraries support in JUnit 5
JUnit 5 Assumptions Examples
Conditional Test Execution in JUnit 5
JUnit 5 Nested Tests Example
JUnit 5 @Tag Annotation example
Test Execution Order in Junit 5
Dependency Injection and Testing in JUnit 5

That’s all about Test Interfaces and Default Methods in JUnit 5
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