added noop_connection for testing

include/matador/sql/backend_provider.hpp

@@ -6,6 +6,7 @@
 #include <memory>
 #include <string>
 #include <unordered_map>
+#include <unordered_set>
 
 namespace matador::sql {
 
@@ -26,28 +27,50 @@ public:
   const dialect& connection_dialect(const std::string &connection_type);
 
 private:
-  struct backend_context {
-    backend_context(const std::string &connection_type,
-                    const std::string &backends_path);
+  struct basic_backend_context {
+    virtual ~basic_backend_context() = default;
+    [[nodiscard]] virtual connection_impl* create(const connection_info&) = 0;
+    virtual void destroy(connection_impl*) = 0;
+    [[nodiscard]] virtual const sql::dialect* dialect() const = 0;
+  };
+
+  class backend_context final : public basic_backend_context {
+  public:
+    explicit backend_context(const std::string &connection_type);
     backend_context(const backend_context&) = delete;
     backend_context& operator=(const backend_context&) = delete;
     backend_context(backend_context&&) noexcept = default;
     backend_context& operator=(backend_context&&) noexcept = default;
-    ~backend_context();
+    ~backend_context() override;
 
+    [[nodiscard]] connection_impl* create(const connection_info&) override;
+    void destroy(connection_impl *conn) override;
+    [[nodiscard]] const class dialect* dialect() const override;
+
+  private:
     typedef connection_impl*(*create_func)(const connection_info&);
     typedef void (*destroy_func)(connection_impl*);
-    typedef const dialect*(*dialect_func)();
+    typedef const class dialect*(*dialect_func)();
 
     create_func create_connection{};
     destroy_func destroy_connection{};
     dialect_func get_dialect{};
     utils::library lib;
   };
+
+  class noop_backend_context final : public basic_backend_context {
+  public:
+    connection_impl *create(const connection_info &info) override;
+    void destroy(connection_impl *impl) override;
+    [[nodiscard]] const sql::dialect *dialect() const override;
+
+  private:
+    std::unordered_set<std::unique_ptr<connection_impl>> noop_connections_;
+  };
+
 private:
-  using backends_t = std::unordered_map<std::string, std::unique_ptr<backend_context>>;
+  using backends_t = std::unordered_map<std::string, std::unique_ptr<basic_backend_context>>;
   backends_t backends_;
-  std::string backends_path_;
 };
 }
 #endif //QUERY_BACKEND_PROVIDER_HPP