Stdin から読み取る Go アプリケーションをテストするにはどうすればよいですか?

<code class="go">package main

import (
    "bufio"
    "fmt"
    "io"
)

// Echo takes an io.Reader and an io.Writer and echoes input to output.
func Echo(r io.Reader, w io.Writer) {
    reader := bufio.NewReader(r)
    for {
        fmt.Print("> ")
        bytes, _, _ := reader.ReadLine()
        if bytes == nil {
            break
        }
        fmt.Fprintln(w, string(bytes))
    }
}

func main() {
    Echo(os.Stdin, os.Stdout)
}</code>

<code class="go">package main

import (
    "bufio"
    "bytes"
    "io"
    "os"
    "testing"
)

func TestEcho(t *testing.T) {
    input := "abc\n"
    reader := bytes.NewBufferString(input)
    writer := &bytes.Buffer{}

    Echo(reader, writer)

    actual := writer.String()
    if actual != input {
        t.Errorf("Wanted: %v, Got: %v", input, actual)
    }
}</code>