public async Task Should_delete_user_in_aad()
        {
            const string USERNAME = EmailData.NON_EXISTENT_USERNAME;

            UserApiClient
            .Setup(x => x.DeleteUserAsync(It.IsAny <string>()))
            .Returns(Task.CompletedTask);

            await UserApiService.DeleteUserInAAD(USERNAME);
        }
        public async Task Should_throw_error_if_failed_to_delete_user_in_aad()
        {
            const string USERNAME = EmailData.NON_EXISTENT_USERNAME;

            UserApiClient
            .Setup(x => x.DeleteUserAsync(It.IsAny <string>()))
            .ThrowsAsync(InternalServerError);

            try
            {
                await UserApiService.DeleteUserInAAD(USERNAME);
            }
            catch (UserApiException ex)
            {
                ex.StatusCode.Should().Be(InternalServerError.StatusCode);
            }
        }