stubbed_env.execute_function will run the script

stubbed_env.execute_function works for scripts that are libraries of functions. Any scripts that include executable code will be executed twice.

Script:
```bash
function another-function(){
  echo "a function"
}
function main(){
    echo "testing"
    another-function
}
main "$@"
```

When trying to test just another-function you will get output to stdout from main as well.

