The Test Engine SPI allows for creating test executors on top of the JVM. In the JUnit 5 framework, there are two Test Engine implementations out of the box:

• The junit-vintage-engine: This allows running JUnit 3 and 4 tests in the JUnit platform.
• The junit-jupiter-engine: This allows running JUnit 5 tests in the JUnit platform.

Moreover, third-party test libraries (for example, Spock, TestNG, and so on) can plug into the JUnit Platform by providing a custom Test Engine. To do that, these frameworks should create its own Test Engine by extending the JUnit 5 interface org.junit.platform.engine.TestEngine. In order to extend this interface, three mandatory methods must be overridden:

• getId: The unique identifier for the test engine.
• discover: The logic to find and filter the test(s).
• execute: The logic to run the previously found test(s).

The following example provides the skeleton for a custom Test Engine:

package io.github.bonigarcia;

import org.junit.platform.engine.EngineDiscoveryRequest;
import org.junit.platform.engine.ExecutionRequest;
import org.junit.platform.engine.TestDescriptor;
import org.junit.platform.engine.TestEngine;
import org.junit.platform.engine.UniqueId;
import org.junit.platform.engine.support.descriptor.EngineDescriptor;

public class MyCustomEngine implements TestEngine {

    public static final String ENGINE_ID = "my-custom-engine";

    @Override
    public String getId() {
        return ENGINE_ID;
    }

    @Override
    public TestDescriptor discover(EngineDiscoveryRequest discoveryRequest,
            UniqueId uniqueId) {
        // Discover test(s) and return a TestDescriptor object
        TestDescriptor testDescriptor = new EngineDescriptor(uniqueId,
                "My test");
        return testDescriptor;
    }

    @Override
    public void execute(ExecutionRequest request) {
        // Use ExecutionRequest to execute TestDescriptor
        TestDescriptor rootTestDescriptor =             
                request.getRootTestDescriptor();
        request.getEngineExecutionListener()
                .executionStarted(rootTestDescriptor);
    }

}