feat: 为执行后端增加独立容量池

internal/backendpool/pool_test.go

@@ -0,0 +1,26 @@
+package backendpool
+
+import "testing"
+
+func TestPoolSeparatesRuntimeCapacityFromDeliveries(t *testing.T) {
+	pool := New(2)
+	if !pool.Acquire("one") || !pool.Acquire("two") || pool.Acquire("three") {
+		t.Fatal("capacity was not enforced")
+	}
+	if !pool.Acquire("one") {
+		t.Fatal("redelivery must be idempotent")
+	}
+	pool.Release("one")
+	if !pool.Acquire("three") || pool.Active() != 2 {
+		t.Fatalf("active=%d", pool.Active())
+	}
+}
+
+func TestRestoreMayTemporarilyExceedReducedCapacity(t *testing.T) {
+	pool := New(1)
+	pool.Restore("one")
+	pool.Restore("two")
+	if pool.Active() != 2 || pool.Acquire("three") {
+		t.Fatalf("active=%d", pool.Active())
+	}
+}