if err != nil {
					if !test.wantErr {
						t.Errorf("%s: %v", path, err)
					}
					sawErr = true
					return nil
				}
				files = append(files, path)
				return nil
			})
			if err != nil {
				t.Errorf("fs.WalkDir error: %v", err)
			}
			if test.wantErr && !sawErr {
				t.Error("succeeded but want error")
			} else if !test.wantErr && sawErr {
				t.Error("unexpected error")

		wantMap  sparseDatas
		wantSize int64
		wantErr  error
	}{{
		input:   makeInput(FormatUnknown, ""),
		wantErr: ErrHeader,
	}, {
		input:    makeInput(FormatGNU, "1234", "fewa"),
		wantSize: 01234,
		wantErr:  ErrHeader,
	}, {
		input:    makeInput(FormatGNU, "0031"),
		wantSize: 031,
	}, {
		input:   makeInput(FormatGNU, "80"),
		wantErr: ErrHeader,
	}, {

		rn, err := r.ReadAt(b, tt.off)
		got := string(b[:rn])
		if got != tt.want {
			t.Errorf("%d. got %q; want %q", i, got, tt.want)
		}
		if fmt.Sprintf("%v", err) != fmt.Sprintf("%v", tt.wanterr) {
			t.Errorf("%d. got error = %v; want %v", i, err, tt.wanterr)
		}
	}
}

func TestReaderAtConcurrent(t *testing.T) {
	// Test for the race detector, to verify ReadAt doesn't mutate
	// any state.
	r := NewReader([]byte("0123456789"))