# Async Tests { #async-tests }

You have already seen how to test your **FastAPI** applications using the provided `TestClient`. Up to now, you have only seen how to write synchronous tests, without using `async` functions.

 * error. If your needs are more complex than {@code SettableFuture} supports, use {@link
 * AbstractFuture}, which offers an extensible version of the API.
 *
 * @author Sven Mawson
 * @since 9.0 (in 1.0 as {@code ValueFuture})
 */
@GwtCompatible
public final class SettableFuture<V extends @Nullable Object>
    extends AbstractFuture.TrustedFuture<V> {
  /**

import java.util.concurrent.ExecutorService;
import junit.framework.TestCase;
import org.jspecify.annotations.NullUnmarked;

/**
 * Test case for {@link ListenableFutureTask}.
 *
 * @author Sven Mawson
 */
@NullUnmarked
public class ListenableFutureTaskTest extends TestCase {

  private ExecutorService exec;

  protected final CountDownLatch runLatch = new CountDownLatch(1);

import java.util.concurrent.atomic.AtomicInteger;
import junit.framework.TestCase;
import org.jspecify.annotations.NullUnmarked;

/**
 * Unit tests for {@link ExecutionList}.
 *
 * @author Nishant Thakkar
 * @author Sven Mawson
 */
@NullUnmarked
public class ExecutionListTest extends TestCase {

  private final ExecutionList list = new ExecutionList();

  public void testRunOnPopulatedList() throws Exception {

    if (seenExceptions == null) {
      seenExceptions = newHashSet();
      addInitialException(seenExceptions);
    }
    return seenExceptions;
  }

  abstract void addInitialException(Set<Throwable> seen);

  final int decrementRemainingAndGet() {
    return --remaining;
  }

  final void clearSeenExceptions() {
    seenExceptions = null;
  }

import org.jspecify.annotations.Nullable;

/**
 * Abstract test case parent for anything implementing {@link ListenableFuture}. Tests the two get
 * methods and the addListener method.
 *
 * @author Sven Mawson
 * @since 10.0
 */
@GwtIncompatible
public abstract class AbstractListenableFutureTest extends TestCase {

  protected CountDownLatch latch;
  protected ListenableFuture<Boolean> future;

  @Override

                });

    // To start, fill up the cache.
    // Each miss both increments the counter and causes the map to grow by one,
    // so until evictions begin, the size of the map is the greatest return
    // value seen so far
    while (cache.getUnchecked(nextRandomKey()) < maximumSize) {}

    requests.set(0);
    misses.set(0);
  }

  @Benchmark
  int time(int reps) {
    int dummy = 0;

import java.util.concurrent.ExecutorService;
import junit.framework.TestCase;
import org.jspecify.annotations.NullUnmarked;

/**
 * Test case for {@link ListenableFutureTask}.
 *
 * @author Sven Mawson
 */
@NullUnmarked
public class ListenableFutureTaskTest extends TestCase {

  private ExecutorService exec;

  protected final CountDownLatch runLatch = new CountDownLatch(1);

import java.util.concurrent.TimeoutException;
import junit.framework.TestCase;
import org.jspecify.annotations.NullUnmarked;

/**
 * Test cases for {@link SettableFuture}.
 *
 * @author Sven Mawson
 */
@NullUnmarked
public class SettableFutureTest extends TestCase {

  private SettableFuture<String> future;
  private ListenableFutureTester tester;

  @Override

import java.util.concurrent.atomic.AtomicInteger;
import junit.framework.TestCase;
import org.jspecify.annotations.NullUnmarked;

/**
 * Unit tests for {@link ExecutionList}.
 *
 * @author Nishant Thakkar
 * @author Sven Mawson
 */
@NullUnmarked
public class ExecutionListTest extends TestCase {

  private final ExecutionList list = new ExecutionList();

  public void testRunOnPopulatedList() throws Exception {