// Special case some of the weird HTTP Header names...
    ImmutableBiMap<String, String> specialCases =
        ImmutableBiMap.<String, String>builder()
            .put("CDN_LOOP", "CDN-Loop")
            .put("ETAG", "ETag")
            .put("SOURCE_MAP", "SourceMap")
            .put("SEC_CH_UA_WOW64", "Sec-CH-UA-WoW64")
            .put("SEC_WEBSOCKET_ACCEPT", "Sec-WebSocket-Accept")

  private static final String ERROR_ADDED_PARALLEL_EDGE =
      "Should not be allowed to add a parallel edge.";
  private static final String ERROR_ADDED_SELF_LOOP =
      "Should not be allowed to add a self-loop edge.";
  static final String ERROR_SELF_LOOP = "self-loops are not allowed";

  @Test
  public void transitiveClosure_directedGraph() {

      assertThat(e).isInstanceOf(ConnectionEvent.ConnectStart::class.java)
    } else {
      eventSequence.forEach loop@{
        when (e.closes(it)) {
          null -> return // no open event
          true -> return // found open event
          false -> return@loop // this is not the open event so continue
        }
      }
      Assertions.fail<Any>("event $e without matching start event")
    }

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**.

So we are going to use that same knowledge to document how the *external API* should look like... by creating the *path operation(s)* that the external API should implement (the ones your API will call).

!!! tip

                collector.checkResolveCall(bindingContext.get(BindingContext.LOOP_RANGE_ITERATOR_RESOLVED_CALL, expression.loopRange))
                collector.checkResolveCall(bindingContext.get(BindingContext.LOOP_RANGE_HAS_NEXT_RESOLVED_CALL, expression.loopRange))
                collector.checkResolveCall(bindingContext.get(BindingContext.LOOP_RANGE_NEXT_RESOLVED_CALL, expression.loopRange))
            }

   * exception goes to the uncaught exception handler.
   */
  private fun interceptorThrowsRuntimeExceptionAsynchronous(network: Boolean) {
    val boom = RuntimeException("boom!")
    addInterceptor(network) { chain: Interceptor.Chain? -> throw boom }
    val executor = ExceptionCatchingExecutor()
    client =
      client.newBuilder()
        .dispatcher(Dispatcher(executor))
        .build()
    val request =

        override fun run() {
          throw RuntimeException("boom!")
        }
      }
    thread.start()
    thread.join()

    assertFailsWith<AssertionError> {
      testRule.afterEach(extensionContext)
    }.also { expected ->
      assertThat(expected).hasMessage("uncaught exception thrown during test")
      assertThat(expected.cause!!).hasMessage("boom!")
    }
  }

!!! tip "Tipp"

  private static final String ERROR_ADDED_PARALLEL_EDGE =
      "Should not be allowed to add a parallel edge.";
  private static final String ERROR_ADDED_SELF_LOOP =
      "Should not be allowed to add a self-loop edge.";
  static final String ERROR_SELF_LOOP = "self-loops are not allowed";

  @Test
  public void transitiveClosure_directedGraph() {

* Select "Python"
* Run the debugger with the option "`Python: Current File (Integrated Terminal)`".

It will then start the server with your **FastAPI** code, stop at your breakpoints, etc.

Here's how it might look:

<img src="/img/tutorial/debugging/image01.png">

---

If you use Pycharm, you can:

* Open the "Run" menu.
* Select the option "Debug...".
* Then a context menu shows up.