What are dynamic tests in JUnit 6 and how do you create them with @TestFactory?

import org.junit.jupiter.api.DynamicTest;
import org.junit.jupiter.api.TestFactory;
import static org.junit.jupiter.api.DynamicTest.dynamicTest;

class DynamicTestsDemo {

    // Basic: generate tests from a list at runtime
    @TestFactory
    Stream<DynamicTest> dynamicAdditionTests() {
        return Stream.of(
            dynamicTest("1 + 1 = 2", () -> assertEquals(2, 1 + 1)),
            dynamicTest("5 + 3 = 8", () -> assertEquals(8, 5 + 3)),
            dynamicTest("-1 + 1 = 0", () -> assertEquals(0, -1 + 1))
        );
    }

    // Useful: load test data from a file, database, or API at runtime
    @TestFactory
    Stream<DynamicTest> testsFromDatabase() {
        return testDataRepository.findAll().stream()
            .map(data -> dynamicTest(
                "Validate: " + data.id(),
                () -> {
                    Result result = service.process(data);
                    assertEquals(data.expectedStatus(), result.status());
                    assertNotNull(result.processedAt());
                }
            ));
    }

    // Dynamic node containers (hierarchical dynamic tests)
    @TestFactory
    Stream<DynamicNode> hierarchical() {
        return Stream.of(
            dynamicContainer("Positive numbers",
                Stream.of(
                    dynamicTest("1 is positive", () -> assertTrue(1 > 0)),
                    dynamicTest("100 is positive", () -> assertTrue(100 > 0))
                )
            )
        );
    }
}