SpamGuard/tests/SpamGuard.Tests/Services/EmailClassifierTests.cs

// tests/SpamGuard.Tests/Services/EmailClassifierTests.cs
namespace SpamGuard.Tests.Services;

using System.Net;
using System.Text.Json;
using Microsoft.Extensions.Logging.Abstractions;
using Microsoft.Extensions.Options;
using SpamGuard.Configuration;
using SpamGuard.Models;
using SpamGuard.Services;
using SpamGuard.State;

public class EmailClassifierTests
{
    private static SpamGuardOptions DefaultOptions => new()
    {
        Claude = new ClaudeOptions
        {
            ApiKey = "test-key",
            Model = "claude-sonnet-4-6",
            MaxBodyLength = 2000
        }
    };

    private static EmailSummary SampleEmail => new(
        Uid: 1,
        From: "spammer@sketchy.com",
        Subject: "Buy now! Limited offer!",
        BodySnippet: "Click here to claim your prize...",
        Date: DateTimeOffset.UtcNow
    );

    [Fact]
    public void BuildPrompt_ContainsSenderAndSubjectAndBody()
    {
        var classifier = new EmailClassifier(
            Options.Create(DefaultOptions),
            new NullLogger<EmailClassifier>(),
            new HttpClient(),
            new OverrideStore(Path.GetTempPath())
        );

        var prompt = classifier.BuildPrompt(SampleEmail);

        Assert.Contains("spammer@sketchy.com", prompt);
        Assert.Contains("Buy now! Limited offer!", prompt);
        Assert.Contains("Click here to claim your prize...", prompt);
    }

    [Fact]
    public void BuildPrompt_TruncatesLongBody()
    {
        var longBody = new string('x', 5000);
        var email = SampleEmail with { BodySnippet = longBody };

        var classifier = new EmailClassifier(
            Options.Create(DefaultOptions),
            new NullLogger<EmailClassifier>(),
            new HttpClient(),
            new OverrideStore(Path.GetTempPath())
        );

        var prompt = classifier.BuildPrompt(email);

        // Body in prompt should be truncated to MaxBodyLength
        Assert.DoesNotContain(longBody, prompt);
    }

    [Fact]
    public void ParseResponse_ValidJson_ReturnsResult()
    {
        var json = """{"classification": "spam", "confidence": 0.95, "reason": "Unsolicited marketing"}""";

        var result = EmailClassifier.ParseResponse(json);

        Assert.NotNull(result);
        Assert.True(result.IsSpam);
        Assert.Equal(0.95, result.Confidence);
        Assert.Equal("Unsolicited marketing", result.Reason);
    }

    [Fact]
    public void ParseResponse_InvalidJson_ReturnsNull()
    {
        var result = EmailClassifier.ParseResponse("not json at all");
        Assert.Null(result);
    }

    [Fact]
    public void ParseResponse_JsonWithMarkdownFencing_ReturnsResult()
    {
        var json = """
            ```json
            {"classification": "legitimate", "confidence": 0.85, "reason": "Normal business email"}
            ```
            """;

        var result = EmailClassifier.ParseResponse(json);

        Assert.NotNull(result);
        Assert.False(result.IsSpam);
    }
}