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capture07.go
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capture07.go
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// Seriál "Programovací jazyk Go"
// https://www.root.cz/serialy/programovaci-jazyk-go/
//
// Padesátá druhá část
// Pomůcky při tvorbě jednotkových testů v jazyce Go
// https://www.root.cz/clanky/pomucky-pri-tvorbe-jednotkovych-testu-v-jazyce-go/
//
// Repositář:
// https://github.com/tisnik/go-root/
//
// Seznam demonstračních příkladů z padesáté druhé části:
// https://github.com/tisnik/go-root/blob/master/article_52/README.md
package main
import (
"bytes"
"fmt"
"io"
"log"
"os"
"sync"
)
func CaptureLog(function func()) (string, error) {
// backup of the real stdout
logOutput := os.Stdout
// temporary replacement for log output
reader, writer, err := os.Pipe()
if err != nil {
return "", err
}
// temporarily replace real log output by the mocked one
defer func() {
log.SetOutput(logOutput)
}()
log.SetOutput(writer)
// channel with captured standard output
captured := make(chan string)
// synchronization object
wg := new(sync.WaitGroup)
// we are going to wait for one goroutine only
wg.Add(1)
go func() {
var buf bytes.Buffer
// goroutine is started -> inform main one via WaitGroup object
wg.Done()
io.Copy(&buf, reader)
captured <- buf.String()
}()
// wait for goroutine to start
wg.Wait()
// provided function that (probably) prints something to standard output
function()
writer.Close()
return <-captured, nil
}
func main() {
str, err := CaptureLog(func() { log.Println("Hello world") })
if err != nil {
panic(err)
}
fmt.Println("Captured logs:")
fmt.Println("-------------------------------")
fmt.Println(str)
fmt.Println("-------------------------------")
}