everything_compile_time.cpp

testing.cpp

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

using namespace std;

// Some instances of events; we're using "public" const data members.
struct UsernameChanged {
    string const username;
};

struct EmailChanged {
    string const email;
};

// Example implementation of a store, where we simply store a username & email
// of a user.
class User {
    string username;
    string email;

public:
    void handle(UsernameChanged const &event) {
        username = event.username;
    }

    void handle(EmailChanged const &event) {
        email = event.email;
    }

    // Some getters
    string getUsername() const {
        return username;
    }

    string getEmail() const {
        return email;
    }
};

template<class Store, class Test>
class Scenario
{
public:
    void run() {
        Store store;
        auto test = static_cast<Test*>(this);

        // Apply given
        apply([&store](auto&&... args){
            (store.handle(args), ...);
        }, test->given());

        // Apply when
        store.handle(test->when());

        // Check then.
        cout << (test->then(store) ? "Test OK!\n" : "Test failed.\n");
    }
};

class UserScenarioTest : public Scenario<User, UserScenarioTest>
{
public:
    auto given()
    {
        return tuple{
            UsernameChanged{"Henk"}, 
            EmailChanged{"[email protected]"}
        };
    }

    auto when()
    {
        return EmailChanged{"[email protected]"};
    }

    bool then(User const &user)
    {
        return user.getEmail() == "[email protected]";
    }
};

int main() {    
    UserScenarioTest test;
    test.run();
}