test: add tests for handler, email, cmd/server, version and enforce 80% coverage

internal/version/version_test.go

@@ -0,0 +1,20 @@
+// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
+// SPDX-License-Identifier: MIT
+
+//go:build linux || freebsd
+
+package version
+
+import "testing"
+
+func TestName(t *testing.T) {
+	if Name != "nuntius" {
+		t.Errorf("Name = %q, want %q", Name, "nuntius")
+	}
+}
+
+func TestVersion(t *testing.T) {
+	if Version == "" {
+		t.Error("Version must not be empty")
+	}
+}