## Add extra information { #add-extra-information }

You can declare extra information in `Field`, `Query`, `Body`, etc. And it will be included in the generated JSON Schema.

You will learn more about adding extra information later in the docs, when learning to declare examples.

/// warning

Extra keys passed to `Field` will also be present in the resulting OpenAPI schema for your application.

You don't want the original dependency to run (nor any of the sub-dependencies it might have).

Instead, you want to provide a different dependency that will be used only during tests (possibly only some specific tests), and will provide a value that can be used where the value of the original dependency was used.

### Use cases: external service { #use-cases-external-service }

    void testWriteSetupWireFormatPreservesBuffer() {
        notifyChange = new NtTransNotifyChange(mockConfig, 0x1234, FILE_NOTIFY_CHANGE_FILE_NAME, false);
        byte[] dst = new byte[20];

        // Fill buffer with test pattern
        for (int i = 0; i < dst.length; i++) {
            dst[i] = (byte) (i & 0xFF);
        }

        int startIndex = 5;

 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *

 * Updating the table can change the contents of those collections, and updating the collections
 * will change the table.
 *
 * <p>All methods that modify the table are optional, and the views returned by the table may or may
 * not be modifiable. When modification isn't supported, those methods will throw an {@link
 * UnsupportedOperationException}.
 *
 * <h3>Implementations</h3>
 *
 * <ul>

//
// Whenever a branch is scanned, it is assumed that it will be un-compacted
// before it hits any of the above limits.
// This will make the branch rebalance itself when scanned if the distribution of objects has changed.

// scanDataFolder will scanner the basepath+cache.Info.Name and return an updated cache.
// The returned cache will always be valid, but may not be updated from the existing.

    """
    Create an invoice.

    This will (let's imagine) let the API user (some external developer) create an
    invoice.

    And this path operation will:

    * Send the invoice to the client.
    * Collect the money from the client.
    * Send a notification back to the API user (the external developer), as a callback.
        * At this point is that the API will somehow send a POST request to the

   *
   * <p><b>Performance note:</b> When feasible, {@code initialCapacity} should be the exact number
   * of values that will be added, if that knowledge is readily available. It is better to guess a
   * value slightly too high than slightly too low. If the value is not exact, the {@link
   * ImmutableLongArray} that is built will very likely occupy more memory than strictly necessary;
   * to trim memory usage, build using {@code builder.build().trimmed()}.

    }

    @Override
    public void execute(Runnable task) {
      // If this operation was successfully cancelled already, calling the runnable will be a noop.
      // This also avoids a race where if outputFuture is cancelled, it will call taskFuture.cancel,
      // which will call newFuture.setFuture(oldFuture), to allow the next task in the queue to run

{* ../../docs_src/background_tasks/tutorial002_an_py310.py hl[13,15,22,25] *}


In this example, the messages will be written to the `log.txt` file *after* the response is sent.

If there was a query in the request, it will be written to the log in a background task.

And then another background task generated at the *path operation function* will write a message using the `email` path parameter.

## Technical Details { #technical-details }