@Override
    public Mono<Void> removeProductFromFavourites(int productId, String userId) {
        return this.favouriteProductRepository.deleteByProductIdAndUserId(productId, userId);
    }
@Test
    void removeProductFromFavourites_ReturnsEmptyMono() {
        // given
        doReturn(Mono.empty()).when(this.favouriteProductRepository)
                .deleteByProductIdAndUserId(1, "5f1d5cf8-cbd6-11ee-9579-cf24d050b47c");

        // when
        StepVerifier.create(this.service.removeProductFromFavourites(1, "5f1d5cf8-cbd6-11ee-9579-cf24d050b47c"))
                // then
                .verifyComplete();

        verify(this.favouriteProductRepository)
                .deleteByProductIdAndUserId(1, "5f1d5cf8-cbd6-11ee-9579-cf24d050b47c");
    }