A test component and system for EntityX (https://github.com/alecthomas/entityx). Does not seem to iterate through any entities from the entities_with_components call. Am I doing something wrong?

gistfile1.cpp

#include <iostream>
#include <string>
#include <vector>

#include <entityx/entityx.h>

std::vector<entityx::Entity> entities_vec;

struct TestComponent : entityx::Component<TestComponent> {
    TestComponent(std::string _name = "test") {
        name = _name;
    }
    std::string name;
};

struct TestSystem : public entityx::System<TestSystem> {
    void update(entityx::ptr<entityx::EntityManager> es, entityx::ptr<entityx::EventManager> events, double dt) override {
        
        //entityx::EntityManager::View entities = es->entities_with_components<TestComponent>();
        entityx::ptr<TestComponent> test;
        for (auto entity : entities_vec) {
            //entityx::ptr<TestComponent> test = entity.component<TestComponent>();
            entity.unpack<TestComponent>(test);
            if (test) { //null test
                std::cout << "test: " << test->name << "\n";
            }
        }
        std::cout << "=====================\n";
    }
};

entityx::ptr<entityx::EventManager> events(new entityx::EventManager());
entityx::ptr<entityx::EntityManager> entities(new entityx::EntityManager(events));

class GameManager : public entityx::Manager {
public:
    
    void configure() {
        system_manager->add<TestSystem>();
        system_manager->configure();
    }

    void initialize() {
        //create any starting entities here.
        
        //create a test entity.
        entityx::Entity testEntity = entities->create();
        testEntity.assign<TestComponent>("test entity from initialize.");
        entities_vec.push_back(testEntity);
        
    }
    
    void update(double dt) {
        //call all the subsystems here, in order.
        system_manager->update<TestSystem>(dt);
    }
};

int main(int argc, const char * argv[])
{

    GameManager* entity_manager = new GameManager();
    entity_manager->configure(); //not sure when this is to be called.
    entity_manager->initialize(); //looks like we have to call this ourselves. Not called by the constructor.
    
    //create a test entity.
    entityx::Entity testEntity = entities->create();
    testEntity.assign<TestComponent>("test entity from main.");
    entities_vec.push_back(testEntity);
    
    // insert code here...
    std::cout << "Hello, World!\n";
    
    float loop_time_s = 1;
    while(true) {
        
        sleep(loop_time_s);
        entity_manager->update(loop_time_s);
        
        std::cout << "looped.\n";
        
    }
    
    return 0;
}

//Current output shows no entities printed:
//GOT:
/*
Hello, World!
=====================
looped.
=====================
looped.
=====================
looped.
*/

//EXPECTED:
/*
Hello, World!
test: test entity from initialize.
test: test entity from main.
=====================
looped.
test: test entity from initialize.
test: test entity from main.
=====================
looped.
test: test entity from initialize.
test: test entity from main.
=====================
looped.
*/

See Rev 1 for my usage of entity querying originally. And, as far as I can tell, should work according to the EntityX examples given.