url        *url.URL
	auth       func() string

	sync.RWMutex // mutex for lastErr
	lastErr      error
	lastErrTime  time.Time
}

type restError string

func (e restError) Error() string {
	return string(e)
}

func (e restError) Timeout() bool {
	return true
}

// Given a string of the form "host", "host:port", or "[ipv6::address]:port",
// return true if the string includes a port.

				mu.Unlock()
			}
		}(i)
	}
	wg.Wait()

	// We already saw write failures, no need to proceed into read's
	if retError != "" {
		return SpeedTestResult{
			Uploads:     totalBytesWritten,
			Downloads:   totalBytesRead,
			UploadTimes: uploadTimes,
			Error:       retError,
		}, nil
	}

	downloadsCtx, downloadsCancel := context.WithTimeout(ctx, opts.duration)
	defer downloadsCancel()

	const text = "abcdefghijklmn\nopqrstuvwxyz\n\r"
	lines := []string{
		"abcdefghijklmn",
		"opqrstuvwxyz",
		"",
	}
	testNoNewline(text, lines, t)
}

var testError = errors.New("testError")

// Test the correct error is returned when the split function errors out.
func TestSplitError(t *testing.T) {
	// Create a split function that delivers a little data, then a predictable error.

import (
	"bytes"
	"errors"
	"fmt"
	"internal/testenv"
	"io"
	"io/fs"
	"maps"
	"math"
	"os"
	"path"
	"path/filepath"
	"reflect"
	"slices"
	"strings"
	"testing"
	"time"
)

type testError struct{ error }

type fileOps []any // []T where T is (string | int64)

// testFile is an io.ReadWriteSeeker where the IO operations performed
// on it must match the list of operations in ops.
type testFile struct {

                    failureUrl.setId("E" + i);
                    failureUrl.setUrl("http://test.com/" + i + ".html");
                    failureUrl.setErrorCount(i);
                    failureUrl.setErrorName("TestError" + i);
                    list.add(failureUrl);
                }
                return list;
            }
        }, FailureUrlBhv.class.getCanonicalName());

						t.Fatalf("test %d, Write() = (%d, %v), want (%d, %v)", i, got, err, tf.wantCnt, tf.wantErr)
					}
				case testReadFrom:
					f := &testFile{ops: tf.ops}
					got, err := tw.readFrom(f)
					if _, ok := err.(testError); ok {
						t.Errorf("test %d, ReadFrom(): %v", i, err)
					} else if got != tf.wantCnt || !equalError(err, tf.wantErr) {
						t.Errorf("test %d, ReadFrom() = (%d, %v), want (%d, %v)", i, got, err, tf.wantCnt, tf.wantErr)

				}
			case testWriteTo:
				f := &testFile{ops: tf.ops}
				got, err := fr.WriteTo(f)
				if _, ok := err.(testError); ok {
					t.Errorf("test %d.%d, WriteTo(): %v", i, j, err)
				} else if got != tf.wantCnt || err != tf.wantErr {
					t.Errorf("test %d.%d, WriteTo() = (%d, %v), want (%d, %v)", i, j, got, err, tf.wantCnt, tf.wantErr)