go-isatty

package main

import (
    "fmt"
    "github.com/mattn/go-isatty"
    "os"
)

func main() {
    if isatty.IsTerminal(os.Stdout.Fd()) {
        fmt.Println("Is Terminal")
    } else if isatty.IsCygwinTerminal(os.Stdout.Fd()) {
        fmt.Println("Is Cygwin/MSYS2 Terminal")
    } else {
        fmt.Println("Is Not Terminal")
    }
}

$ go get github.com/mattn/go-isatty