test: покрыть NopAuthenticator, GenerateSelfSignedCert, HandshakeSem

Минимальное покрытие для заготовки auth и хелперов dtlsdial:
- NopAuthenticator.Authenticate возвращает (Anonymous, nil)
- GenerateSelfSignedCert выдаёт рабочий сертификат с приватным ключом
- HandshakeSem блокирует захват при заполнении и уважает отмену ctx

Также документирует на Authenticator, что интерфейс stream-ориентирован; auth
UDP-режима получит отдельный token-based интерфейс.

internal/auth/auth.go

@@ -20,6 +20,11 @@ const Anonymous TenantID = ""
 // A nil error with [Anonymous] means the connection is accepted in
 // non-multi-tenant mode. Any non-nil error must be treated as a rejection
 // and the caller must close conn.
+//
+// This interface is stream-oriented: it consumes a net.Conn and is intended
+// for bondserver/tcpfwdserver wiring. UDP-mode auth (when needed) will get
+// a separate interface taking a token []byte read out-of-band from the
+// handshake, since udpserver has no per-tenant stream abstraction.
 type Authenticator interface {
 	Authenticate(ctx context.Context, conn net.Conn) (TenantID, error)
 }

internal/auth/auth_test.go

@@ -0,0 +1,13 @@
+package auth
+
+import "testing"
+
+func TestNopAuthenticatorReturnsAnonymous(t *testing.T) {
+	tenant, err := NopAuthenticator{}.Authenticate(t.Context(), nil)
+	if err != nil {
+		t.Fatalf("NopAuthenticator.Authenticate: %v", err)
+	}
+	if tenant != Anonymous {
+		t.Fatalf("tenant = %q want Anonymous (%q)", tenant, Anonymous)
+	}
+}

internal/transport/dtlsdial/handshakesem_test.go

@@ -0,0 +1,39 @@
+package dtlsdial
+
+import (
+	"context"
+	"errors"
+	"net"
+	"testing"
+	"time"
+)
+
+// TestHandshakeSemBlocksWhenFull verifies the contract: when HandshakeSem
+// is at capacity, a new Dial blocks on the slot acquisition and respects
+// ctx cancellation. Validates the bound that prevents unbounded concurrent
+// handshakes under high -n values.
+func TestHandshakeSemBlocksWhenFull(t *testing.T) {
+	sem := make(chan struct{}, 1)
+	sem <- struct{}{} // pre-fill: cap = 1, full
+
+	d := &Dialer{HandshakeSem: sem}
+
+	pc, err := net.ListenPacket("udp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatalf("listen: %v", err)
+	}
+	defer pc.Close()
+	peer := &net.UDPAddr{IP: net.ParseIP("127.0.0.1"), Port: 1}
+
+	ctx, cancel := context.WithTimeout(context.Background(), 50*time.Millisecond)
+	defer cancel()
+
+	start := time.Now()
+	_, err = d.Dial(ctx, pc, peer)
+	if !errors.Is(err, context.DeadlineExceeded) {
+		t.Fatalf("err = %v want DeadlineExceeded", err)
+	}
+	if elapsed := time.Since(start); elapsed < 40*time.Millisecond {
+		t.Fatalf("Dial returned too fast (%v); expected to block on sem", elapsed)
+	}
+}

internal/transport/dtlsdial/selfsigned_test.go

@@ -0,0 +1,16 @@
+package dtlsdial
+
+import "testing"
+
+func TestGenerateSelfSignedCert(t *testing.T) {
+	cert, err := GenerateSelfSignedCert()
+	if err != nil {
+		t.Fatalf("GenerateSelfSignedCert: %v", err)
+	}
+	if len(cert.Certificate) == 0 {
+		t.Fatal("certificate chain is empty")
+	}
+	if cert.PrivateKey == nil {
+		t.Fatal("private key is nil")
+	}
+}