单元测试 FluentEmail in .NET 5 使用 xUnit 和 Moq

Question

I'm trying to unit test FluentEmail , but I keep getting null in the send response.

This is how it's set up in the ConfigureServices method:

// Set email service using FluentEmail
services.AddFluentEmail("sender@test.com")
        // For Fluent Email to find _Layout.cshtml, just mention here where your views are.
        .AddRazorRenderer(@$"{Directory.GetCurrentDirectory()}/Views/")
        .AddSmtpSender("smtp.somecompanyname.com", 25)
        .AddSmtpSender(new System.Net.Mail.SmtpClient() { });

Now the email service looks like this:

public class FluentEmailService : IFluentEmailService
{
    private readonly IFluentEmail _fluentEmail;
    private readonly ILogger<FluentEmailService> _logger;
    public FluentEmailService(ILogger<FluentEmailService> logger, IFluentEmail fluentEmail)
    {
        _logger = logger;
        _fluentEmail = fluentEmail;
    }

    public async Task<SendResponse> SendEmailAsync<TModel>(string subject, string razorTemplatePath, TModel model, string semicolonSeparatedEmailRecipients)
    {
        try
        {
            var sendResponse = await _fluentEmail
                            .To(semicolonSeparatedEmailRecipients)
                            .Subject(subject)
                            .UsingTemplateFromFile(razorTemplatePath, model)
                            .SendAsync();
            return sendResponse;
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Failed to send email. Check exception for more information.");
            return new SendResponse() { ErrorMessages = new string[] { ex.Message } };
        }
    }
}

My test method looks like this:

[Fact]
public async Task Can_Verify_FluentEmail_WORKS_Async()
{
    // ARRANGE
    var mockFluentEmail = new Mock<IFluentEmail>();

    mockFluentEmail.Setup(m => m.To(It.IsAny<string>())).Returns(mockFluentEmail.Object);
    mockFluentEmail.Setup(m => m.Subject(It.IsAny<string>())).Returns(mockFluentEmail.Object);
    mockFluentEmail.Setup(m => m.UsingTemplateFromFile(It.IsAny<string>(), It.IsAny<It.IsAnyType>(), It.IsAny<bool>())).Returns(mockFluentEmail.Object);

    //Create FluentEmail service using fake logger and IFluentEmail
    var fakeLogger = Mock.Of<ILogger<FluentEmailService>>();
    var fluentEmailService = new FluentEmailService(fakeLogger, mockFluentEmail.Object);

    // ACT
    var sendResponse = await fluentEmailService.SendEmailAsync("Test Subject", "Some Path", It.IsAny<It.IsAnyType>(), "Some Recipient");
    
    // ASSERT
    Assert.NotNull(sendResponse);
    Assert.True(sendResponse.Successful);
    mockFluentEmail.Verify(f => f.To("Some Recipient"), Times.Once(), "Recipient should be set as: 'Some Recipient'.");
    mockFluentEmail.Verify(f => f.Subject("Test Subject"), Times.Once, "Subject should be set as: 'Test Subject'.");
    mockFluentEmail.Verify(f => f.UsingTemplateFromFile("Some Path", It.IsAny<It.IsAnyType>(), It.IsAny<bool>()), Times.Once, "Path should be set as: 'Some Path'.");
    mockFluentEmail.Verify(f => f.SendAsync(null), Times.Once, "1 email should be sent.");
}

The test always fails because I get null as the sendResponse .

Can someone please tell me if I'm doing this correctly?

Answer 1

It is probably because of last function call SendAsync is not mocked and therefore returning null by default.

Since it is async call, it makes sense to use ReturnsAsync instead of Returns .

ReturnsAsync should also return an actual SendResponse :

//...

SendResponse expectedSendResponse = new SendResponse();

mockFluentEmail
   .Setup(m => m.SendAsync(null))
   .ReturnsAsync(expectedSendResponse);

//...