Testing CLI arguments in go - unit-testing

Question

I want to test some CLI routines in go that are run in the main() function purely, they are just exercises that I'm doing, but I want to make tests on them!
So for example how can I pass arguments to table test this king of algorithm?
package main
import (
"bufio"
"fmt"
"os"
"strconv"
)
func main() {
var f *os.File
f = os.Stdin
defer f.Close()
scanner := bufio.NewScanner(f)
for scanner.Scan() {
if scanner.Text() == "STOP" || scanner.Text() == "stop" {
break
}
n, err := strconv.ParseInt(scanner.Text(), 10, 64)
if err == nil {
fmt.Printf("Number formatted: %d\n", n)
} else {
fmt.Println(err.Error())
}
}
}
I put the code on playground too for better help!
https://play.golang.org/p/JgrQ2yFogNs
Thanks in advance!

Answer 1

You need to create a function which input and output channels as params. It should read and write to these params. Following is an example:
main.go
package main
import (
"bufio"
"fmt"
"io"
"os"
"strconv"
)
func main() {
var f *os.File
f = os.Stdin
defer f.Close()
run (os.Stdin, f)
}
func run(in io.Reader, out io.Writer) {
scanner := bufio.NewScanner(in)
for scanner.Scan() {
if scanner.Text() == "STOP" || scanner.Text() == "stop" {
break
}
n, err := strconv.ParseInt(scanner.Text(), 10, 64)
if err == nil {
fmt.Printf("Number formatted: %d\n", n)
} else {
fmt.Println(err.Error())
}
}
}
main_test.go
package main
import (
"bytes"
"fmt"
"testing"
)
func TestRun(t *testing.T){
var command, result bytes.Buffer
fmt.Fprintf(&command, "10\n")
fmt.Fprintf(&command, "stop\n")
run(&command, &result)
got := result.String()
//test for contents of "got"
fmt.Println(got)
}
Now you can run the following on a command line.
go test

Answer 2

Strictly speaking, you don't need to use Go for this. When I'm looking at writing a CLI tool I break out of main as soon as possible with functions and structs the unit test those in the usual way.
To make sure that all the CLI arguments and file system buts are plumbed in correctly I've been using https://github.com/bats-core/bats-core to run the command and check the fully built tool.
You can see an example of how I've done this at https://github.com/dnnrly/abbreviate
Perhaps not the answer you're looking for but it's been working well for me.