///

### Step 4: define the **path operation function** { #step-4-define-the-path-operation-function }

This is our "**path operation function**":

* **path**: is `/`.
* **operation**: is `get`.
* **function**: is the function below the "decorator" (below `@app.get("/")`).

{* ../../docs_src/first_steps/tutorial001_py310.py hl[7] *}

This is a Python function.

///

/// tip | Consejo

Si quieres llamar a funciones `async` en tus pruebas además de enviar requests a tu aplicación FastAPI (por ejemplo, funciones asincrónicas de bases de datos), echa un vistazo a las [Pruebas Asincrónicas](../advanced/async-tests.md) en el tutorial avanzado.

///

## Separando pruebas { #separating-tests }

public class MapComputeIfPresentTester<K, V> extends AbstractMapTester<K, V> {

  @MapFeature.Require(SUPPORTS_PUT)
  public void testComputeIfPresent_supportedAbsent() {
    assertNull(
        "computeIfPresent(notPresent, function) should return null",
        getMap()
            .computeIfPresent(
                k3(),
                (k, v) -> {
                  throw new AssertionFailedError();
                }));
    expectUnchanged();

#!/bin/bash

set -e
# Enable tracing if set.
[ -n "$BASH_XTRACEFD" ] && set -x

function _init() {
	## All binaries are static make sure to disable CGO.
	export CGO_ENABLED=0

	## List of architectures and OS to test coss compilation.
	SUPPORTED_OSARCH="linux/ppc64le linux/mips64 linux/amd64 linux/arm64 linux/s390x darwin/arm64 darwin/amd64 freebsd/amd64 windows/amd64 linux/arm linux/386 netbsd/amd64 linux/mips openbsd/amd64 linux/riscv64"
}

import com.google.common.base.Function;
import org.jspecify.annotations.NullMarked;
import org.jspecify.annotations.Nullable;

/**
 * Test cases for {@link Tables#transformValues}.
 *
 * @author Jared Levy
 */
@GwtCompatible
@NullMarked
public class TablesTransformValuesTest extends AbstractTableTest<Character> {

  private static final Function<@Nullable String, @Nullable Character> FIRST_CHARACTER =

package com.google.common.collect;

import com.google.common.annotations.GwtCompatible;
import com.google.common.base.Function;
import java.util.ListIterator;
import org.jspecify.annotations.Nullable;

/**
 * An iterator that transforms a backing list iterator; for internal use. This avoids the object
 * overhead of constructing a {@link Function} for internal methods.
 *
 * @author Louis Wasserman
 */
@GwtCompatible

package com.google.common.collect;

import com.google.common.annotations.GwtCompatible;
import com.google.common.base.Function;
import java.util.ListIterator;
import org.jspecify.annotations.Nullable;

/**
 * An iterator that transforms a backing list iterator; for internal use. This avoids the object
 * overhead of constructing a {@link Function} for internal methods.
 *
 * @author Louis Wasserman
 */
@GwtCompatible

            ws.onmessage = function(event) {
                var messages = document.getElementById('messages')
                var message = document.createElement('li')
                var content = document.createTextNode(event.data)
                message.appendChild(content)
                messages.appendChild(message)
            };
            function sendMessage(event) {

import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Set;
import java.util.function.BiFunction;
import java.util.function.Function;
import java.util.function.Predicate;

/**
 * This should be removed when https://bugs.openjdk.org/browse/JDK-8323729
 * is released in our minimum JDK.
 */
class ImmutableCollections {

///

## Create a middleware { #create-a-middleware }

To create a middleware you use the decorator `@app.middleware("http")` on top of a function.

The middleware function receives:

* The `request`.
* A function `call_next` that will receive the `request` as a parameter.
    * This function will pass the `request` to the corresponding *path operation*.
    * Then it returns the `response` generated by the corresponding *path operation*.