Testing Stdout with go and ginkgo

Question

here I am making my first steps in go trying to do BDD on a go command line app. I am using Ginkgo, which wraps testing.go and lets you do more expressive BDD. https://github.com/onsi/ginkgo

I am having issues in reading the stdout to do an assertion on it.

Found that on pkg/testing example do stub the output before running but I can not find the way to read that output: http://golang.org/src/pkg/testing/example.go

This is what I would like to do:

cli.go

 package cli
  
 import "fmt"
  
 func Run() {
        fmt.Println("Running cli")
 }

cli_test.go

package cli_test

import (
        . "github.com/altoros/bosh_deployer_cli/lib/cli"

        . "github.com/onsi/ginkgo"
        . "github.com/onsi/gomega"
)

var _ = Describe("Cli", func() {
        It("should parse update stemcell flag", func() {
                Run()
                Expect(stdout).To(Equal("running cli"))
        })
})

Answer 1

Testing Stdout can be tricky. You have multiple choice.

You can override os.Stdout during your test: (think to check the errors)

var _ = Describe("Cli", func() {
        It("should parse update stemcell flag", func() {
                r, w, _ := os.Pipe()
                tmp := os.Stdout
                defer func() {
                        os.Stdout = tmp
                }()
                os.Stdout = w
                go func() {
                        Run()
                        w.Close()
                }()
                stdout, _ := ioutil.ReadAll(r)
                Expect(string(stdout)).To(Equal("Running cli\n"))
        })
})

or you can pass a writer to your function:

cli.go

package cli

import (
        "fmt"
        "io"
)

func Run(w io.Writer) {
        fmt.Fprintln(w, "Running cli")
}

cli_test.go

package cli_test

import (
        . "cli"
        "io"
        "io/ioutil"

        . "github.com/onsi/ginkgo"
        . "github.com/onsi/gomega"
)

var _ = Describe("Cli", func() {
        It("should parse update stemcell flag", func() {
                r, w := io.Pipe()
                go func() {
                        Run(w)
                        w.Close()
                }()
                stdout, _ := ioutil.ReadAll(r)
                Expect(string(stdout)).To(Equal("Running cli\n"))
        })
})

main.go

package main

import (
        "cli"
        "os"
)

func main() {
        cli.Run(os.Stdout)
}