[Go] How to test urfave/cli command

go.mod

module how/to/test/urfave/cli/command

go 1.19

require github.com/urfave/cli/v2 v2.20.2

require (
	github.com/cpuguy83/go-md2man/v2 v2.0.2 // indirect
	github.com/russross/blackfriday/v2 v2.1.0 // indirect
	github.com/xrash/smetrics v0.0.0-20201216005158-039620a65673 // indirect
)

how-to-test_urfave-cli_command.go

package main

import (
	"fmt"
	"os"

	"github.com/urfave/cli/v2"
)

func main() {
	err := NewApp().Run(os.Args)
	if err != nil {
		fmt.Fprintln(os.Stderr, err)
		os.Exit(1)
	}
}

func NewApp() *cli.App {
	app := cli.NewApp()
	app.Name = "hello-world"
	app.Action = func(c *cli.Context) error {
		fmt.Fprintf(c.App.Writer, "Hello, World!")
		return nil
	}
	app.Commands = []*cli.Command{
		Greeting,
	}

	return app
}

var Greeting *cli.Command = &cli.Command{
	Name: "greet",
	Flags: []cli.Flag{
		&cli.StringFlag{
			Name:    "name",
			Aliases: []string{"n"},
			Value:   "nameless",
		},
	},
	Action: func(c *cli.Context) error {
		fmt.Fprintf(c.App.Writer, "Hello, %s!!", c.String("name"))
		return nil
	},
}

how-to-test_urfave-cli_command_test.go

package main

import (
	"bytes"
	"flag"
	"testing"

	"github.com/urfave/cli/v2"
)

func TestNewApp(t *testing.T) {
	var output bytes.Buffer // capture output
	app := NewApp()
	app.Writer = &output
	set := flag.NewFlagSet("test", 0)
	_ = set.Parse([]string{"foo", "bar"})

	// Exercise
	err := app.Run([]string{"-foo"})

	// Verify
	if err != nil {
		t.Error(err)
		t.FailNow()
	}
	expected := "Hello, World!"
	if output.String() != expected {
		t.Errorf("expected '%s' but got '%s'", expected, output.String())
	}
}

func TestApp_Greeting(t *testing.T) {
	t.Run("with name", func(t *testing.T) {
		var output bytes.Buffer // capture output

		app := NewApp()
		app.Writer = &output

		cCtx := cli.NewContext(app, nil, nil)
		args := []string{"greet", "--name", "foo"}

		// Exercise
		err := app.Command("greet").Run(cCtx, args...)

		// Verify
		if err != nil {
			t.Error(err)
			t.FailNow()
		}
		expected := "Hello, foo!!"
		if output.String() != expected {
			t.Errorf("expected '%s' but got '%s'", expected, output.String())
		}
	})
	t.Run("nameless", func(t *testing.T) {
		var output bytes.Buffer // capture output

		app := NewApp()
		app.Writer = &output

		cCtx := cli.NewContext(app, nil, nil)
		args := []string{"greet"}

		// Exercise
		err := app.Command("greet").Run(cCtx, args...)

		// Verify
		if err != nil {
			t.Error(err)
			t.FailNow()
		}
		expected := "Hello, nameless!!"
		if output.String() != expected {
			t.Errorf("expected '%s' but got '%s'", expected, output.String())
		}
	})
}