private async Task WriteOperation_IfBodyContainsOnlySpaces_ShouldThrowPostValidationException(WriteOperationTypes operationType)
        {
            var service = CreateTestingService();
            var postWithWhiteSpacesBody = new Post(Guid.NewGuid(), "  ");

            switch (operationType)
            {
            case WriteOperationTypes.Add:
                await Assert.ThrowsAsync <PostValidationException>(async() => await service.AddAsync(postWithWhiteSpacesBody));

                break;

            case WriteOperationTypes.Update:
                await Assert.ThrowsAsync <PostValidationException>(async() => await service.UpdateAsync(postWithWhiteSpacesBody));

                break;
            }
        }
        private async Task WriteOperation_IfIdEmpty_ShouldThrowPostValidationException(WriteOperationTypes operationType)
        {
            var service           = CreateTestingService();
            var postWithEmptyBody = new Post(Guid.Empty, "write post body");

            switch (operationType)
            {
            case WriteOperationTypes.Add:
                await Assert.ThrowsAsync <PostValidationException>(async() => await service.AddAsync(postWithEmptyBody));

                break;

            case WriteOperationTypes.Update:
                await Assert.ThrowsAsync <PostValidationException>(async() => await service.UpdateAsync(postWithEmptyBody));

                break;
            }
        }