Testing

JVM Testing & Microbenchmark Tools

Test-driven code on the JVM rests on a durable core of tooling: a test framework (JUnit 5 or TestNG), an assertion library (AssertJ), and a mocking library (Mockito). Around that core, Testcontainers lets you spin up real infrastructure for integration tests, and JMH is the only sane way to microbenchmark code on a modern JIT-compiled JVM.

For performance and load, Gatling and k6 cover scenario-based load testing. Because the JVM's JIT compiler makes naive benchmarking meaningless, JMH deserves special attention whenever you need a measured number.

What you'll find here: Unit tests: JUnit 5, TestNG, AssertJ, Mockito · Integration tests with real containers: Testcontainers · Microbenchmarks without JIT pitfalls: JMH · Load & API testing: Gatling, k6

Testing tools

JUnit 5
The current standard testing framework for the JVM: annotations, dynamic tests, and the Jupiter extension model; runs on the JUnit Platform.
open-sourceEPL-2.0
TestNG
A test framework inspired by JUnit that adds parallel execution, data providers and rich configuration; a strong alternative when those matter.
open-sourceApache-2.0
AssertJ
A fluent, rich assertion library for writing readable tests with descriptive failure messages; the standard companion to JUnit 5.
open-sourceApache-2.0
Mockito
The most widely used mocking framework on the JVM; creates fake objects, stubs methods and verifies interactions in tests.
open-sourceMIT
Testcontainers
Spins up real Docker infrastructure (databases, message brokers, browsers) for integration tests, then tears it down; makes repeatable integration testing practical.
open-sourceApache-2.0
JMH (Java Microbenchmark Harness)
OpenJDK's harness for writing correct microbenchmarks — it deals with warm-up, dead-code elimination and JIT effects so your numbers mean something.
open-sourceGPLv2 w/ CE
Gatling
A high-performance, scenario-based load-testing tool that records realistic user flows and reports rich KPIs; easy to script in Scala or Java.
open-sourceApache-2.0 (core)
Grafana k6
A developer-friendly load-testing tool scripted in JavaScript that executes with a Go engine; widely used for API and k8s load testing.
open-sourceAGPL-3.0 (OSS core)

In-depth guides in this category

JMH
JMH tutorial: set up, write and run correct microbenchmarks, avoid JIT dead-code elimination and warm-up traps, and read the results.