## Write the callback documentation code { #write-the-callback-documentation-code }

This code won't be executed in your app, we only need it to *document* how that *external API* should look like.

But, you already know how to easily create automatic documentation for an API with **FastAPI**.

    assertThrows(IllegalArgumentException.class, () -> multiset.add(KEY, COUNT_TO_ADD));
  }

  /**
   * Simulate some of the races that can happen on add. We can't easily simulate the race that
   * happens when an {@link AtomicInteger#compareAndSet} fails, but we can simulate the case where
   * the putIfAbsent returns a non-null value, and the case where the replace() of an observed zero

        when(httpSession.getAttribute("NtlmHttpChal")).thenReturn(null);

        // For this test, we'll simulate that no auth header means we should challenge
        // Since we can't mock the internal transport operations easily without real network,
        // we'll test the simpler case where no NTLM negotiation is needed
        when(request.getHeader("Authorization")).thenReturn(null);

        filter.doFilter(request, response, filterChain);

That way, it behaves almost as if it was just a global variable. But as it uses a dependency function, then we can override it easily for testing.

`@lru_cache` is part of `functools` which is part of Python's standard library, you can read more about it in the [Python docs for `@lru_cache`](https://docs.python.org/3/library/functools.html#functools.lru_cache).

* Validate **complex structures**:
    * Use of hierarchical Pydantic models, Python `typing`’s `List` and `Dict`, etc.
    * And validators allow complex data schemas to be clearly and easily defined, checked and documented as JSON Schema.
    * You can have deeply **nested JSON** objects and have them all validated and annotated.
* **Extensible**:

* Dependency Injection system.

It doesn't use a data validation, serialization and documentation third-party library like Pydantic, it has its own. So, these data type definitions would not be reusable as easily.

It requires a little bit more verbose configurations. And as it is based on WSGI (instead of ASGI), it is not designed to take advantage of the high performance provided by tools like Uvicorn, Starlette and Sanic.

                          type: string
                          example: "Docs » Open Source Enterprise Search Server: Fess Commercial Support Open Source Enterprise Search Server: Fess What is Fess ? Fess is very powerful and easily deployable Enterprise Search Server. ..."
                        host:
                          type: string
                          format: hostname
                          example: "fess.codelibs.org"

                if (getInputs() == null) {
                    return super.getInputsValue();
                }
                return super.getInputsValue();
            }
        };

        // Since we can't easily set inputs to null, test with empty array
        String[] emptyInputs = {};
        CharMappingItem emptyItem = new CharMappingItem(1L, emptyInputs, "output");
        assertEquals("", emptyItem.getInputsValue());
    }

        when(mockFuture.actionGet(anyLong(), any(TimeUnit.class))).thenReturn(mockHealthResponse);

        // Should not throw NullPointerException
        try {
            // Note: We can't easily test connect() fully without mocking createClient()
            // This test verifies the null check logic indirectly
            final String[] indices = fesenClient.targetIndices != null ? fesenClient.targetIndices : new String[0];

But once you know the basic information of **HTTPS for developers** you can easily combine and configure different tools to help you manage everything in a simple way.