go-cli-advertised-subcommand-unregistered

Answer

The bug: main.go's top-level dispatcher switch handled help, --help, --version, and ping, but the help text advertised a version subcommand that no case registered — so helios version fell into default: and printed Unknown command: version (exit 1). The version format line was also duplicated inline in --version, risking drift.

Fix 1 — extract the shared versionLine() formatter (main.go):

const version = "0.1.0"

// versionLine returns the canonical version string. Both the --version
// flag path and the version subcommand path print exactly this line, so
// the two paths can never drift apart. It is the testable seam: main()
// exits via os.Exit on failure, so this formatter is what unit tests pin.
func versionLine() string {
    return fmt.Sprintf("helios version %s", version)
}

Fix 2 — register the version case and route both paths through the helper:

    switch args[0] {
    case "help", "-h", "--help":
        fmt.Print(usage)
    case "--version":
        fmt.Println(versionLine())
    case "version":                    // ← added case
        fmt.Println(versionLine())
    case "ping":
        fmt.Println("pong")
    default:
        fmt.Printf("Unknown command: %s\n", args[0])
        fmt.Print(usage)
        os.Exit(1)
    }

Fix 3 — table-test the seam (version_test.go), since the dispatcher exits via os.Exit on the failure path:

func TestVersionLine(t *testing.T) {
    const want = "helios version 0.1.0"
    tests := []struct {
        name  string
        check func(got string) bool
    }{
        {"is non-empty", func(got string) bool { return got != "" }},
        {"starts with the binary name", func(got string) bool { return strings.HasPrefix(got, "helios ") }},
        {"embeds the version number", func(got string) bool { return strings.Contains(got, version) }},
        {"matches the exact canonical line", func(got string) bool { return got == want }},
        {"has no trailing newline (caller adds it)", func(got string) bool { return !strings.HasSuffix(got, "\n") }},
        {"has no leading whitespace", func(got string) bool { return !strings.HasPrefix(got, " ") }},
    }
    for _, tt := range tests {
        t.Run(tt.name, func(t *testing.T) {
            if got := versionLine(); !tt.check(got) {
                t.Errorf("versionLine() = %q (want %q)", got, want)
            }
        })
    }
}