Cobra + Viper Golang How to test subcommands?

I am developing an web app with Go. So far so good, but now I am integrating Wercker as a CI tool and started caring about testing. But my app relies heavily on Cobra/Viper configuration/flags/environment_variables scheme, and I do not know how to properly init Viper values before running my test suite. Any help would be much appreciated.

When I use Cobra/Viper or any other combination of CLI helpers, my way of doing this is to have the CLI tool run a function whose sole purpose will be to get arguments and pass them to another method who will do the actual work.

Here is a short (and dumb) example using Cobra :

package main

import (
        "fmt"
        "os"

        "github.com/spf13/cobra"
)

func main() {
        var Cmd = &cobra.Command{
                Use:   "boom",
                Short: "Explode all the things!",
                Run:   Boom,
        }

        if err := Cmd.Execute(); err != nil {
                fmt.Println(err)
                os.Exit(-1)
        }
}

func Boom(cmd *cobra.Command, args []string) {
        boom(args...)
}

func boom(args ...string) {
        for _, arg := range args {
                println("boom " + arg)
        }
}

Here, the Boom function is hard to test, but the boom one is easy.

You can see another (non-dumb) example of this here (and the correspond test here).