En este caso, podrías querer documentar cómo esa API externa *debería* verse. Qué *path operation* debería tener, qué cuerpo debería esperar, qué response debería devolver, etc.

## Una aplicación con callbacks

Veamos todo esto con un ejemplo.

Imagina que desarrollas una aplicación que permite crear facturas.

    /** The key of the configuration. e.g. 50 */
    String RESPONSE_MAX_TITLE_LENGTH = "response.max.title.length";

    /** The key of the configuration. e.g. 100 */
    String RESPONSE_MAX_SITE_PATH_LENGTH = "response.max.site.path.length";

    /** The key of the configuration. e.g. true */

import org.codelibs.fess.mylasta.mail.TestmailPostcard;
import org.codelibs.fess.util.ComponentUtil;
import org.lastaflute.core.mail.Postbox;
import org.lastaflute.web.Execute;
import org.lastaflute.web.response.HtmlResponse;
import org.lastaflute.web.ruts.process.ActionRuntime;

import jakarta.annotation.Resource;

/**
 * Admin action for General settings.
 *
 */

     */
    @Override
    public void doFilter(final ServletRequest request, final ServletResponse response, final FilterChain chain)
            throws IOException, ServletException {
        final HttpServletRequest req = (HttpServletRequest) request;
        final HttpServletResponse resp = (HttpServletResponse) response;
        NtlmPasswordAuthentication ntlm = negotiate(req, resp, false);

        if (ntlm == null) {

import org.lastaflute.core.message.MessageManager;
import org.lastaflute.core.time.TimeManager;
import org.lastaflute.db.dbflute.accesscontext.AccessContextArranger;
import org.lastaflute.web.TypicalAction;
import org.lastaflute.web.response.ActionResponse;
import org.lastaflute.web.ruts.process.ActionRuntime;
import org.lastaflute.web.servlet.request.RequestManager;
import org.lastaflute.web.servlet.request.ResponseManager;

    server.start()

    val call1 =
      client.newCall(
        Request
          .Builder()
          .url(server.url("/"))
          .build(),
      )
    call1.execute().use { response -> response.body.string() }

    listener.shouldClose = true
    // Large headers are a likely reason the servers would cut off the connection before it completes sending
    // request headers.

 */
package jcifs.internal.witness;

/**
 * Represents a witness heartbeat response as defined in MS-SWN specification.
 * Contains the result of a witness heartbeat request.
 */
public class WitnessHeartbeatResponse {
    /**
     * Creates a new witness heartbeat response.
     */
    public WitnessHeartbeatResponse() {
        // Default constructor
    }

 */
package jcifs.internal.witness;

/**
 * Represents a witness registration response as defined in MS-SWN specification.
 * Contains the result of a witness registration request.
 */
public class WitnessRegisterResponse {
    /**
     * Creates a new witness register response.
     */
    public WitnessRegisterResponse() {
        // Default constructor
    }

    void testSetupResponse() {
        // Arrange
        doNothing().when(negotiationResponse).setupResponse(response);

        // Act
        negotiationResponse.setupResponse(response);

        // Assert
        verify(negotiationResponse).setupResponse(response);
    }

    @Test
    @DisplayName("Test setupResponse with null")
    void testSetupResponseWithNull() {
        // Arrange

        Smb2FlushResponse response = request.createResponse(mockContext, request);

        assertNotNull(response);

        // Verify response has correct config
        Field configField = ServerMessageBlock2.class.getDeclaredField("config");
        configField.setAccessible(true);
        Configuration responseConfig = (Configuration) configField.get(response);
        assertEquals(mockConfig, responseConfig);