@TestInstance Lifecycle Comparison

This tutorial demonstrates the practical differences between PER_METHOD and PER_CLASS lifecycles.

Key Comparison Points

• PER_METHOD: New instance per test method, high isolation
• PER_CLASS: Single instance shared, maintains state

Side-by-Side Example

PER_METHOD Example

package com.logicbig.example;

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

@TestInstance(TestInstance.Lifecycle.PER_METHOD)
public class PerMethodExampleTest {

    private String instanceId = this.toString();
    private int operationCount = 0;

    @Test
    void testDatabaseConnection() {
        operationCount++;
        System.out.println("PER_METHOD - TestDatabaseConnection");
        System.out.println("  Instance ID: " + instanceId);
        System.out.println("  Operation Count: " + operationCount);
    }

    @Test
    void testDataInsert() {
        operationCount++;
        System.out.println("PER_METHOD - TestDataInsert");
        System.out.println("  Instance ID: " + instanceId);
        System.out.println("  Operation Count: " + operationCount);
    }

    @Test
    void testDataQuery() {
        operationCount++;
        System.out.println("PER_METHOD - TestDataQuery");
        System.out.println("  Instance ID: " + instanceId);
        System.out.println("  Operation Count: " + operationCount);
    }
}

PER_CLASS Example

package com.logicbig.example;

import org.junit.jupiter.api.*;

@TestInstance(TestInstance.Lifecycle.PER_CLASS)
public class PerClassExampleTest {

    private String instanceId = this.toString();
    private int operationCount = 0;
    private StringBuilder auditLog = new StringBuilder();

    @BeforeAll
    void setupSharedResources() {
        System.out.println("PER_CLASS - SetupSharedResources");
        System.out.println("  Shared Instance ID: " + instanceId);
        auditLog.append("Setup completed\n");
    }

    @Test
    void testDatabaseConnection() {
        operationCount++;
        auditLog.append("Database connected - Operation: " + operationCount + "\n");
        System.out.println("PER_CLASS - TestDatabaseConnection");
        System.out.println("  Instance ID: " + instanceId);
        System.out.println("  Operation Count: " + operationCount);
    }

    @Test
    void testDataInsert() {
        operationCount++;
        auditLog.append("Data inserted - Operation: " + operationCount + "\n");
        System.out.println("PER_CLASS - TestDataInsert");
        System.out.println("  Instance ID: " + instanceId);
        System.out.println("  Operation Count: " + operationCount);
    }

    @Test
    void testDataQuery() {
        operationCount++;
        auditLog.append("Data queried - Operation: " + operationCount + "\n");
        System.out.println("PER_CLASS - TestDataQuery");
        System.out.println("  Instance ID: " + instanceId);
        System.out.println("  Operation Count: " + operationCount);
    }

    @AfterAll
    void cleanupAndReport() {
        System.out.println("PER_CLASS - CleanupAndReport");
        System.out.println("  Final Operation Count: " + operationCount);
        System.out.println("  Audit Log:\n" + auditLog.toString());
    }
}

Running Both Example

mvn test

Output

D:\example-projects\junit-5\test-instance\junit-5-test-instance-lifecycle>mvn test
[INFO] Scanning for projects...
[INFO] 
[INFO] --------< com.logicbig.example:junit-5-test-instance-lifecycle >--------
[INFO] Building junit-5-test-instance-lifecycle 1.0-SNAPSHOT
[INFO]   from pom.xml
[INFO] --------------------------------[ jar ]---------------------------------
[INFO] 
[INFO] --- resources:3.3.1:resources (default-resources) @ junit-5-test-instance-lifecycle ---
[WARNING] Using platform encoding (Cp1252 actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] skip non existing resourceDirectory D:\example-projects\junit-5\test-instance\junit-5-test-instance-lifecycle\src\main\resources
[INFO] 
[INFO] --- compiler:3.11.0:compile (default-compile) @ junit-5-test-instance-lifecycle ---
[INFO] No sources to compile
[INFO] 
[INFO] --- resources:3.3.1:testResources (default-testResources) @ junit-5-test-instance-lifecycle ---
[WARNING] Using platform encoding (Cp1252 actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] skip non existing resourceDirectory D:\example-projects\junit-5\test-instance\junit-5-test-instance-lifecycle\src\test\resources
[INFO] 
[INFO] --- compiler:3.11.0:testCompile (default-testCompile) @ junit-5-test-instance-lifecycle ---
[INFO] Nothing to compile - all classes are up to date
[INFO] 
[INFO] --- surefire:3.2.5:test (default-test) @ junit-5-test-instance-lifecycle ---
[INFO] Using auto detected provider org.apache.maven.surefire.junitplatform.JUnitPlatformProvider
[INFO] 
[INFO] -------------------------------------------------------
[INFO]  T E S T S
[INFO] -------------------------------------------------------
[INFO] Running com.logicbig.example.PerClassExampleTest
PER_CLASS - SetupSharedResources
  Shared Instance ID: com.logicbig.example.PerClassExampleTest@6f96c77
PER_CLASS - TestDatabaseConnection
  Instance ID: com.logicbig.example.PerClassExampleTest@6f96c77
  Operation Count: 1
PER_CLASS - TestDataInsert
  Instance ID: com.logicbig.example.PerClassExampleTest@6f96c77
  Operation Count: 2
PER_CLASS - TestDataQuery
  Instance ID: com.logicbig.example.PerClassExampleTest@6f96c77
  Operation Count: 3
PER_CLASS - CleanupAndReport
  Final Operation Count: 3
  Audit Log:
Setup completed
Database connected - Operation: 1
Data inserted - Operation: 2
Data queried - Operation: 3

[INFO] Tests run: 3, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.092 s -- in com.logicbig.example.PerClassExampleTest
[INFO] Running com.logicbig.example.PerMethodExampleTest
PER_METHOD - TestDatabaseConnection
  Instance ID: com.logicbig.example.PerMethodExampleTest@399f45b1
  Operation Count: 1
PER_METHOD - TestDataInsert
  Instance ID: com.logicbig.example.PerMethodExampleTest@478190fc
  Operation Count: 1
PER_METHOD - TestDataQuery
  Instance ID: com.logicbig.example.PerMethodExampleTest@79e2c065
  Operation Count: 1
[INFO] Tests run: 3, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.012 s -- in com.logicbig.example.PerMethodExampleTest
[INFO] 
[INFO] Results:
[INFO] 
[INFO] Tests run: 6, Failures: 0, Errors: 0, Skipped: 0
[INFO] 
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  2.904 s
[INFO] Finished at: 2025-12-05T14:20:39+08:00
[INFO] ------------------------------------------------------------------------

As seen above, PER_METHOD, instance variables are reinitialized for every test, whereas with PER_CLASS Instance variables retain their values across different test methods showing they are created and initialized only once.

Example Project

Dependencies and Technologies Used:

• junit-jupiter-engine 6.0.1 (Module "junit-jupiter-engine" of JUnit)
   Version Compatibility: 5.0.0 - 6.0.1Version List
  ×

  Version compatibilities of junit-jupiter-engine with this example:

  • 5.0.0
  • 5.0.1
  • 5.0.2
  • 5.0.3
  • 5.1.0
  • 5.1.1
  • 5.2.0
  • 5.3.0
  • 5.3.1
  • 5.3.2
  • 5.4.0
  • 5.4.1
  • 5.4.2
  • 5.5.0
  • 5.5.1
  • 5.5.2
  • 5.6.0
  • 5.6.1
  • 5.6.2
  • 5.6.3
  • 5.7.0
  • 5.7.1
  • 5.7.2
  • 5.8.0
  • 5.8.1
  • 5.8.2
  • 5.9.0
  • 5.9.1
  • 5.9.2
  • 5.9.3
  • 5.10.0
  • 5.10.1
  • 5.10.2
  • 5.10.3
  • 5.10.4
  • 5.10.5
  • 5.11.0
  • 5.11.1
  • 5.11.2
  • 5.11.3
  • 5.11.4
  • 5.12.0
  • 5.12.1
  • 5.12.2
  • 5.13.0
  • 5.13.1
  • 5.13.2
  • 5.13.3
  • 5.13.4
  • 5.14.0
  • 5.14.1
  • 6.0.0
  • 6.0.1

  Versions in green have been tested.

• JDK 25
• Maven 3.9.11