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

internal/handler/contact.go

@@ -20,23 +20,34 @@ import (
 	"sourcedock.dev/petrbalvin/nuntius/pkg/contactform"
 )
 
+// formSender is the interface for delivering a submission.
+type formSender interface {
+	Send(req contactform.Request) error
+}
+
+// subscriberStorer persists newsletter subscribers.
+// storage.NewsletterStore satisfies this interface.
+type subscriberStorer interface {
+	Append(sub storage.Subscriber) error
+}
+
 // ContactHandler serves one or more contact forms, dispatched by URL path.
 // Each form has its own sender, rate limiter, CORS allowlist, and honeypot.
 // Newsletter-type forms also get a per-form subscriber store.
 type ContactHandler struct {
 	forms      map[string]*config.Form
-	senders    map[string]*email.FormSender
+	senders    map[string]formSender
 	rateLimits map[string]*rateLimiter
-	stores     map[string]*storage.NewsletterStore
+	stores     map[string]subscriberStorer
 }
 
 // New constructs a ContactHandler that serves all forms defined in cfg.
 func New(cfg *config.Config) *ContactHandler {
 	h := &ContactHandler{
 		forms:      make(map[string]*config.Form, len(cfg.Forms)),
-		senders:    make(map[string]*email.FormSender, len(cfg.Forms)),
+		senders:    make(map[string]formSender, len(cfg.Forms)),
 		rateLimits: make(map[string]*rateLimiter, len(cfg.Forms)),
-		stores:     make(map[string]*storage.NewsletterStore, len(cfg.Forms)),
+		stores:     make(map[string]subscriberStorer, len(cfg.Forms)),
 	}
 	for i := range cfg.Forms {
 		f := &cfg.Forms[i]