t.Errorf("ReadLine returned both data and error: %s", err)
			}
			if isPrefix {
				t.Errorf("ReadLine returned prefix")
			}
			if err != nil {
				if err != io.EOF {
					t.Fatalf("Got unknown error: %s", err)
				}
				break
			}
			if want := testOutput[done : done+len(line)]; !bytes.Equal(want, line) {
				t.Errorf("Bad line at stride %d: want: %x got: %x", stride, want, line)
			}