Move testlib to internal

internal/testlib/capture_output.go

@@ -0,0 +1,42 @@
+package testlib
+
+import (
+	"bytes"
+	"io"
+	"os"
+	"strings"
+)
+
+func CaptureStdout(callback func()) string {
+	return captureOutput(&os.Stdout, callback)
+}
+
+func CaptureStderr(callback func()) string {
+	return captureOutput(&os.Stderr, callback)
+}
+
+func captureOutput(filefp **os.File, callback func()) string {
+	oldFp := *filefp
+
+	defer func() {
+		*filefp = oldFp
+	}()
+
+	reader, writer, _ := os.Pipe()
+	buf := &bytes.Buffer{}
+	closeChan := make(chan bool)
+
+	go func() {
+		io.Copy(buf, reader) // nolint: errcheck
+		close(closeChan)
+	}()
+
+	*filefp = writer
+
+	callback()
+
+	writer.Close()
+	<-closeChan
+
+	return strings.TrimSpace(buf.String())
+}