val coordinatorTask = waitingCoordinatorTask ?: error("no coordinator waiting")
          currentTask = coordinatorTask
          taskRunner.notifyAll()
        }
      }

    // Let the coordinator process its interruption.
    runTasks()
  }

  /** Ask a single task to proceed. Used by the test thread only. */
  fun runNextTask() {
    taskRunner.assertLockNotHeld()

                  CollectionFeature.RESTRICTS_ELEMENTS,
                  ListFeature.SUPPORTS_SET)
              .createTestSuite());
    }
    return suite;
  }

  // Test generators.  To let the GWT test suite generator access them, they need to be
  // public named classes with a public default constructor.

  public static final class FloatsAsListGenerator extends TestFloatListGenerator {
    @Override

                  CollectionFeature.RESTRICTS_ELEMENTS,
                  ListFeature.SUPPORTS_SET)
              .createTestSuite());
    }
    return suite;
  }

  // Test generators.  To let the GWT test suite generator access them, they need to be
  // public named classes with a public default constructor.

  public static final class FloatsAsListGenerator extends TestFloatListGenerator {
    @Override

                  CollectionFeature.RESTRICTS_ELEMENTS,
                  ListFeature.SUPPORTS_SET)
              .createTestSuite());
    }
    return suite;
  }

  // Test generators.  To let the GWT test suite generator access them, they need to be
  // public named classes with a public default constructor.

  public static final class IntsAsListGenerator extends TestIntegerListGenerator {
    @Override

   */
  @SuppressWarnings("unchecked")
  public static <T extends @Nullable Object> Collector<T, ?, T> onlyElement() {
    return (Collector) ONLY_ELEMENT;
  }

  /**
   * This atrocity is here to let us report several of the elements in the stream if there were more
   * than one, not just two.
   */
  @SuppressWarnings("EmptyList") // ImmutableList doesn't support nullable element types

  @Synchronized private fun initUncaughtException(throwable: Throwable) {
    if (uncaughtException == null) {
      uncaughtException = throwable
    }
  }

  fun ensureAllConnectionsReleased() {
    testClient?.let {
      val connectionPool = it.connectionPool

      connectionPool.evictAll()
      if (connectionPool.connectionCount() > 0) {
        // Minimise test flakiness due to possible race conditions with connections closing.

       * running under Jelly Bean or higher. But it seems safest to check.
       */
      if (version < jellyBean) {
        return new ThrowingCreator();
      }

      // Don't merge these catch() blocks, let alone use ReflectiveOperationException directly:
      // b/65343391
    } catch (NoSuchFieldException e) {
      // The JELLY_BEAN field doesn't exist because we're running on a version before Jelly Bean :)

          shift += 24;
          len += 3;
        } else {
          int codePoint = Character.codePointAt(input, i);
          if (codePoint == c) {
            // not a valid code point; let the JDK handle invalid Unicode
            return hashBytes(input.toString().getBytes(charset));
          }
          i++;
          buffer |= codePointToFourUtf8Bytes(codePoint) << shift;

        // We will return a composite buffer from the test when building the full packet.
        // To keep this helper simple, return base and let the caller append/pad and inject ctx.
        return base;
    }

    /**
     * Build a full SMB2 packet combining header and provided body, optionally injecting context bytes.
     */

So, what we will do next is add the code to document how that *external API* should look like to receive the callback from *your API*.

That documentation will show up in the Swagger UI at `/docs` in your API, and it will let external developers know how to build the *external API*.

This example doesn't implement the callback itself (that could be just a line of code), only the documentation part.

/// tip