Java testing is not one framework, it is a stack

Most teams treat Java testing as a single-framework problem: pick one tool, learn it well, and bend every kind of test to fit it. We treat it as a stack, where the framework changes with the layer under test. The difference shows up the moment someone tries to unit test through a browser or verify a microservice contract with a UI automation tool.

The reason is division of labor, not preference. JUnit 5 verifies units of logic in isolation, with parameterized tests, dynamic test discovery, and extension points that keep test code as maintainable as the code it tests. Mockito removes real dependencies from that picture entirely, so a unit test proves the logic and nothing else. Selenium exists for a different job: driving an actual browser, because no unit test can tell you whether a page behaves correctly across different browsers and environments.

Match the tool to the layer

In practice this means stacking frameworks by what they are actually testing. TestNG adds grouping and parallel execution on top of the unit layer, so tests that would otherwise run one at a time can run together, across machines. RestAssured and WireMock cover the API layer: one sends requests and asserts on the response, the other simulates the external services a test should not have to depend on. Pact adds a consumer-driven contract check between microservices, catching a broken integration before a deployment instead of after one. Arquillian goes further still, running integration tests inside the real Java EE container rather than a simulation of it.

• Unit and mocking coverage from JUnit 5 and Mockito, so logic is proven correct before any dependency is involved.
• Parallel, cross-browser execution from TestNG and Selenium, so the same suite runs faster and covers more ground.
• API, virtualization, and contract checks from RestAssured, WireMock, and Pact, so integration breaks surface before deployment, not after.
• Human-readable specifications from Cucumber and Spock, so test intent stays clear to people who never open the code.

The right framework is the one built for the layer you are testing, not the one you already know.

Choose for the job, not the brand

None of this is about collecting frameworks for their own sake. It is about matching the tool to the question actually being asked: does this unit behave correctly, does this endpoint return the right response, does this service still honor its contract after a change. Teams that make that match well catch defects earlier and spend less time chasing failures that were never really about the code. Teams that force one framework to answer every question end up debugging the framework instead of the product.