}
                }
                if ( log.isDebugEnabled() ) {
                    log.debug("Failures " + failCount.get() + " wrote " + writeCount.get() + " read " + readCnt);
                }
                assertEquals("Read less than we wrote", writeCount.get(), readCnt);
                assertEquals(n, failCount.get() + writeCount.get());
            }
            finally {
                f.delete();

Being able to use asynchronous functions in your tests could be useful, for example, when you're querying your database asynchronously. Imagine you want to test sending requests to your FastAPI application and then verify that your backend successfully wrote the correct data in the database, while using an async database library.

The process that happens when your API app calls the *external API* is named a "callback". Because the software that the external developer wrote sends a request to your API and then your API *calls back*, sending a request to an *external API* (that was probably created by the same developer).

                            if ( log.isDebugEnabled() ) {
                                log.debug(
                                    String.format(
                                        "Wrote %d bytes (%d chunks, last partial write %d)",
                                        r.getTotalBytesWritten(),
                                        r.getChunksWritten(),
                                        r.getChunkBytesWritten()));

	}

again:
	nextOut, ok := w.buffer[w.nextOffset]
	if ok {
		n, err = w.w.Write(nextOut)
		delete(w.buffer, w.nextOffset)
		w.nextOffset += int64(n)
		if n != len(nextOut) {
			return 0, fmt.Errorf("expected write size %d but wrote %d bytes", len(nextOut), n)
		}
		if err != nil {
			return 0, err
		}
		goto again
	}

	return len(b), nil
}

	}
}

type teststringwriter struct {
	write       string
	writeString string
}

func (w *teststringwriter) Write(b []byte) (int, error) {
	w.write += string(b)
	return len(b), nil
}

func (w *teststringwriter) WriteString(s string) (int, error) {
	w.writeString += s
	return len(s), nil
}

func (w *teststringwriter) check(t *testing.T, write, writeString string) {
	t.Helper()

		fmt.Println("No bytes missing.")
		out += ".complete"
	}
	m.mapped = m.mapped[:lastValid+1]
	err = os.WriteFile(out, m.mapped, os.ModePerm)
	if err != nil {
		return err
	}
	fmt.Println("Wrote output to", out)
	return nil
}

func combineCrossVer(all map[string][]string, baseName string) error {
	names := make([][]string, 0)
	/// part, verID, file
	files := make([]map[string][]string, 0)

	}
	for i := 0; i < chunks; i++ {
		_, err := f.Write(chunk)
		if err != nil {
			t.Fatal("write chunk:", err)
		}
	}
	if frag := int(size % chunkSize); frag > 0 {
		_, err := f.Write(chunk[:frag])
		if err != nil {
			t.Fatal("write chunk:", err)
		}
	}
	end := []byte("END\n")
	_, err = f.Write(end)
	if err != nil {
		t.Fatal("write end:", err)
	}
	if err := w.Close(); err != nil {

	// Call the ServeHTTP to execute the handler.
	apiRouter.ServeHTTP(rec, req)

	ctx, cancel := context.WithCancel(GlobalContext)
	defer cancel()

	// Now check if we actually wrote to backend (regardless of the response
	// returned by the server).
	z := obj.(*erasureServerPools)
	xl := z.serverPools[0].sets[0]
	erasureDisks := xl.getDisks()

	// Call the ServeHTTP to execute the handler.
	apiRouter.ServeHTTP(rec, req)

	ctx, cancel := context.WithCancel(GlobalContext)
	defer cancel()

	// Now check if we actually wrote to backend (regardless of the response
	// returned by the server).
	z := obj.(*erasureServerPools)
	xl := z.serverPools[0].sets[0]
	erasureDisks := xl.getDisks()