import junit.framework.TestCase;
import org.jspecify.annotations.NullUnmarked;

/**
 * @param <S> the source or sink type
 * @param <T> the data type (byte[] or String)
 * @param <F> the factory type
 * @author Colin Decker
 */
@AndroidIncompatible // TODO(b/230620681): Make this available (even though we won't run it).
@NullUnmarked
public class SourceSinkTester<S, T, F extends SourceSinkFactory<S, T>> extends TestCase {

/**
 * A generator of {@code TestSuite} instances for testing {@code CharSource} implementations.
 * Generates tests of all methods on a {@code CharSource} given various inputs the source is
 * expected to contain.
 *
 * @author Colin Decker
 */
@AndroidIncompatible // TODO(b/230620681): Make this available (even though we won't run it).
@NullUnmarked
public class CharSourceTester extends SourceSinkTester<CharSource, String, CharSourceFactory> {

import junit.framework.TestCase;
import org.jspecify.annotations.NullUnmarked;
import org.jspecify.annotations.Nullable;

/**
 * Base test case class for I/O tests.
 *
 * @author Chris Nokleberg
 * @author Colin Decker
 */
@NullUnmarked
public abstract class IoTestCase extends TestCase {

  private static final Logger logger = Logger.getLogger(IoTestCase.class.getName());

  static final String I18N =

import java.io.IOException;
import java.nio.CharBuffer;
import junit.framework.TestCase;
import org.jspecify.annotations.NullUnmarked;

/**
 * Tests for {@link CharSequenceReader}.
 *
 * @author Colin Decker
 */
@NullUnmarked
public class CharSequenceReaderTest extends TestCase {

  public void testReadEmptyString() throws IOException {
    assertReadsCorrectly("");
  }

 * controls the order in which events are dispatched, while the executor controls how (i.e. on which
 * thread) the subscriber is actually called when an event is dispatched to it.
 *
 * @author Colin Decker
 */
abstract class Dispatcher {

  /**
   * Returns a dispatcher that queues events that are posted reentrantly on a thread that is already

import java.util.List;
import org.jspecify.annotations.Nullable;

/**
 * Provides utility methods for working with character streams.
 *
 * @author Chris Nokleberg
 * @author Bin Zhu
 * @author Colin Decker
 * @since 1.0
 */
@J2ktIncompatible
@GwtIncompatible
public final class CharStreams {

  // 2K chars (4K bytes)
  private static final int DEFAULT_BUF_SIZE = 0x800;

You can define dependencies that in turn can define dependencies themselves.

In the end, a hierarchical tree of dependencies is built, and the **Dependency Injection** system takes care of solving all these dependencies for you (and their sub-dependencies) and providing (injecting) the results at each step.

For example, let's say you have 4 API endpoints (*path operations*):

* `/items/public/`

import java.util.stream.Stream;
import junit.framework.TestSuite;
import org.jspecify.annotations.NullUnmarked;

/**
 * Tests for the default implementations of {@code CharSource} methods.
 *
 * @author Colin Decker
 */
@NullUnmarked
public class CharSourceTest extends IoTestCase {

  @AndroidIncompatible // Android doesn't understand suites whose tests lack default constructors.
  public static TestSuite suite() {

import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.CopyOnWriteArraySet;
import org.jspecify.annotations.Nullable;

/**
 * Registry of subscribers to a single event bus.
 *
 * @author Colin Decker
 */
final class SubscriberRegistry {

  /**
   * All registered subscribers, indexed by event type.
   *
   * <p>The {@link CopyOnWriteArraySet} values make it easy and relatively lightweight to get an

import java.util.stream.Stream;
import junit.framework.TestSuite;
import org.jspecify.annotations.NullUnmarked;

/**
 * Tests for the default implementations of {@code CharSource} methods.
 *
 * @author Colin Decker
 */
@NullUnmarked
public class CharSourceTest extends IoTestCase {

  @AndroidIncompatible // Android doesn't understand suites whose tests lack default constructors.
  public static TestSuite suite() {