feat(multiplayer): add regional allocation budget

server/allocator/budget_test.go

@@ -0,0 +1,72 @@
+package allocator
+
+import (
+	"errors"
+	"sync"
+	"testing"
+	"time"
+)
+
+func TestFixedWindowBudgetLimitsEachRegionAndResets(t *testing.T) {
+	now := time.Unix(1000, 0).UTC()
+	budget, err := NewFixedWindowBudget(2, time.Minute)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for i := 0; i < 2; i++ {
+		if err := budget.Allow("EU", now); err != nil {
+			t.Fatalf("EU attempt %d: %v", i, err)
+		}
+	}
+	if err := budget.Allow("EU", now); !errors.Is(err, ErrAllocationBudgetExceeded) {
+		t.Fatalf("third EU attempt = %v, want budget error", err)
+	}
+	if err := budget.Allow("NA", now); err != nil {
+		t.Fatalf("NA should have an independent budget: %v", err)
+	}
+	if err := budget.Allow("EU", now.Add(time.Minute)); err != nil {
+		t.Fatalf("EU after window: %v", err)
+	}
+}
+
+func TestFixedWindowBudgetIsAtomicUnderConcurrentAttempts(t *testing.T) {
+	budget, err := NewFixedWindowBudget(7, time.Minute)
+	if err != nil {
+		t.Fatal(err)
+	}
+	now := time.Unix(1000, 0).UTC()
+	var wg sync.WaitGroup
+	var mu sync.Mutex
+	allowed := 0
+	for i := 0; i < 64; i++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			if budget.Allow("EU", now) == nil {
+				mu.Lock()
+				allowed++
+				mu.Unlock()
+			}
+		}()
+	}
+	wg.Wait()
+	if allowed != 7 {
+		t.Fatalf("allowed=%d, want exactly 7", allowed)
+	}
+}
+
+func TestFixedWindowBudgetRejectsInvalidConfigurationAndInput(t *testing.T) {
+	if _, err := NewFixedWindowBudget(0, time.Minute); err == nil {
+		t.Fatal("zero limit accepted")
+	}
+	if _, err := NewFixedWindowBudget(1, 0); err == nil {
+		t.Fatal("zero window accepted")
+	}
+	budget, _ := NewFixedWindowBudget(1, time.Minute)
+	if err := budget.Allow("APAC", time.Unix(1000, 0)); err == nil {
+		t.Fatal("unknown region accepted")
+	}
+	if err := budget.Allow("EU", time.Time{}); err == nil {
+		t.Fatal("zero time accepted")
+	}
+}