fix util::stack_vector

test/util/stack_vector.cpp

@@ -0,0 +1,20 @@
+#include <gtest/gtest.h>
+#include <string>
+
+#include "util/stack_vector.hpp"
+
+using namespace util;
+
+TEST(util, stack_vector) {
+    stack_vector<std::string, 4> vec;
+    vec.push_back("hello");
+    vec.push_back("world");
+    vec.push_back("?");
+    ASSERT_EQ(3, vec.size());
+    vec.pop_back();
+    ASSERT_EQ(2, vec.size());
+    vec.clear();
+    ASSERT_EQ(0, vec.size());
+    ASSERT_TRUE(vec.empty());
+    vec.push_back("test");
+}