Injecting random data into Jupiter tests

RandomParameterExtensionTest.java

import org.codefx.demo.junit5.extensions.RandomParameterExtensionTest.RandomProvider;
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.Test;
import org.junit.jupiter.api.extension.ExtendWith;
import org.junit.jupiter.api.extension.ExtensionContext;
import org.junit.jupiter.api.extension.ParameterContext;
import org.junit.jupiter.api.extension.ParameterResolutionException;
import org.junit.jupiter.api.extension.ParameterResolver;
import org.junit.jupiter.api.extension.TestExecutionExceptionHandler;
import org.junit.jupiter.api.extension.TestExtensionContext;

import java.util.Map;
import java.util.Optional;
import java.util.Random;
import java.util.concurrent.ConcurrentHashMap;

@ExtendWith(RandomProvider.class)
class RandomParameterExtensionTest {

	@BeforeAll
	static void beforeAll_1(SeededRandom r) {
		System.out.println("Before all #1: " + r.seed());
	}

	@BeforeAll
	static void beforeAll_2(SeededRandom r) {
		System.out.println("Before all #2: " + r.seed());
	}

	@BeforeEach
	void beforeEach_1(SeededRandom r) {
		System.out.println("Before each #1: " + r.seed());
	}

	@BeforeEach
	void beforeEach_2(SeededRandom r) {
		System.out.println("Before each #2: " + r.seed());
	}

	@Test
	void test(SeededRandom r) {
		System.out.println("Test: " + r.seed());
	}

	@Test
	void failingTest(SeededRandom r) {
		System.out.println("Failing Test: " + r.seed());
		throw new IllegalArgumentException("FAIL!");
	}

	@AfterEach
	void afterEach_1(SeededRandom r) {
		System.out.println("After each #1: " + r.seed());
	}

	@AfterEach
	void afterEach_2(SeededRandom r) {
		System.out.println("After each #2: " + r.seed());
	}

	@AfterAll
	static void afterAll_1(SeededRandom r) {
		System.out.println("After all #1: " + r.seed());
	}

	@AfterAll
	static void afterAll_2(SeededRandom r) {
		System.out.println("After all #2: " + r.seed());
	}

	static class RandomProvider implements ParameterResolver, TestExecutionExceptionHandler {
		
		private final Map<String, SeededRandom> randoms = new ConcurrentHashMap<>();

		@Override
		public boolean supports(
				ParameterContext parameterContext, ExtensionContext extensionContext)
				throws ParameterResolutionException {
			Class<?> targetType = parameterContext.getParameter().getType();
			return targetType == Random.class || targetType == SeededRandom.class;
		}

		@Override
		public Object resolve(
				ParameterContext parameterContext, ExtensionContext extensionContext)
				throws ParameterResolutionException {
			return randoms.computeIfAbsent(extensionContext.getUniqueId(), SeededRandom::create);
		}

		@Override
		public void handleTestExecutionException(
				TestExtensionContext context, Throwable throwable) throws Throwable {
			String seed = Optional.ofNullable(randoms.get(context.getUniqueId()))
					.map(SeededRandom::seed)
					.map(s -> "seed " + s)
					.orElse("unknown seed");
			System.out.println("Exception occurred in test based on " + seed);
		}

	}
	
	static class SeededRandom extends Random {

		private static Random seeder = new Random();

		private final String testId;
		private final long seed;

		private SeededRandom(String testId, long seed) {
			super(seed);
			this.testId = testId;
			this.seed = seed;
		}

		static SeededRandom create(String testId) {
			return new SeededRandom(testId, seeder.nextLong());
		}

		String testId() {
			return testId;
		}

		long seed() {
			return seed;
		}

	}
	
}