如何编写写入stdin的Go测试？

Question

Say that I have a simple application that reads lines from stdin and simply echoes it back to stdout. For example:

package main

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

func main() {
    reader := bufio.NewReader(os.Stdin)
    for {
        fmt.Print("> ")
        bytes, _, err := reader.ReadLine()
        if err == io.EOF {
            os.Exit(0)
        }
        fmt.Println(string(bytes))
    }
}

I would like to write a test case that writes to stdin and then compares the output to the input. For example:

package main

import (
    "bufio"
    "io"
    "os"
    "os/exec"
    "testing"
)

func TestInput(t *testing.T) {
    subproc := exec.Command(os.Args[0])
    stdin, _ := subproc.StdinPipe()
    stdout, _ := subproc.StdoutPipe()
    defer stdin.Close()

    input := "abc
"

    subproc.Start()
    io.WriteString(stdin, input)
    reader := bufio.NewReader(stdout)
    bytes, _, _ := reader.ReadLine()
    output := string(bytes)
    if input != output {
        t.Errorf("Wanted: %v, Got: %v", input, output)
    }
    subproc.Wait()
}

Running go test -v gives me the following:

=== RUN   TestInput
--- FAIL: TestInput (3.32s)
    echo_test.go:25: Wanted: abc
        , Got: --- FAIL: TestInput (3.32s)
FAIL
exit status 1

I'm obviously doing something incorrect here. How should I go about testing this type of code?

Answer 1

Here is an example that writes to stdin and reads from stdout. Note that it does not work because the output contains "> " at first. Still, you can modify it to suit your needs.

func TestInput(t *testing.T) {
    subproc := exec.Command("yourCmd")
    input := "abc
"
    subproc.Stdin = strings.NewReader(input)
    output, _ := subproc.Output()

    if input != string(output) {
        t.Errorf("Wanted: %v, Got: %v", input, string(output))
    }
    subproc.Wait()
}