GoogleMock example

Since GoogleMock is part of GoogleTest, we will present them together:

#include "merchants/reviews.h"

#include <gmock/gmock.h>

#include <merchants/visited_merchant_history.h>

#include "fake_customer_review_store.h"

namespace {

class mock_visited_merchant : public i_visited_merchant {
 public:
  explicit mock_visited_merchant(fake_customer_review_store &store,
                                 merchant_id_t id)
      : review_store_{store},
        review_{store.get_review_for_merchant(id).value()} {
    ON_CALL(*this, post_rating).WillByDefault([this](stars s) {
      review_.rating = s;
      review_store_.post_review(review_);
    });
    ON_CALL(*this, get_rating).WillByDefault([this] { return review_.rating; });
  }

  MOCK_METHOD(stars, get_rating, (), (override));
  MOCK_METHOD(void, post_rating, (stars s), (override));

 private:
  fake_customer_review_store &review_store_;
  review review_;
};

} // namespace

class history_with_one_rated_merchant...