llm-pii-poc/tests/PiiRedaction.Core.Tests/Detection/CompositePiiDetectorTests.cs

using FluentAssertions;
using PiiRedaction.Core.Abstractions;
using PiiRedaction.Core.Detection;
using PiiRedaction.Core.Models;

namespace PiiRedaction.Core.Tests.Detection;

[TestFixture]
public sealed class CompositePiiDetectorTests
{
    [Test]
    public void Detect_AdjacentSpans_KeepsBothEntities()
    {
        var composite = new CompositePiiDetector([new FixedDetector(
            new PiiEntity(PiiEntityType.Email, "a@b.co", 0, 6, PiiDetectionSource.Regex),
            new PiiEntity(PiiEntityType.Phone, "9876543210", 6, 10, PiiDetectionSource.Regex))]);

        var entities = composite.Detect("abcdef9876543210padding");

        entities.Should().HaveCount(2);
    }

    [Test]
    public void Detect_NestedSpan_KeepsLongerSpan()
    {
        var composite = new CompositePiiDetector([new FixedDetector(
            new PiiEntity(PiiEntityType.Aadhaar, "123456789012", 0, 12, PiiDetectionSource.Regex),
            new PiiEntity(PiiEntityType.Phone, "4567890123", 2, 10, PiiDetectionSource.Regex))]);

        var entities = composite.Detect("123456789012");

        entities.Should().ContainSingle(entity => entity.Type == PiiEntityType.Aadhaar);
    }

    [Test]
    public void Detect_OverlappingSameStart_LongerSpanWins()
    {
        var composite = new CompositePiiDetector([new FixedDetector(
            new PiiEntity(PiiEntityType.LoanNumber, "LN-456789", 0, 9, PiiDetectionSource.Domain),
            new PiiEntity(PiiEntityType.Phone, "456789", 3, 6, PiiDetectionSource.Regex))]);

        var entities = composite.Detect("LN-456789");

        entities.Should().ContainSingle(entity => entity.Type == PiiEntityType.LoanNumber);
    }

    [Test]
    public void Detect_OverlappingDifferentPriority_DomainBeatsRegex()
    {
        var composite = new CompositePiiDetector([new FixedDetector(
            new PiiEntity(PiiEntityType.LoanNumber, "LN-456789", 0, 9, PiiDetectionSource.Domain),
            new PiiEntity(PiiEntityType.Phone, "456789", 0, 6, PiiDetectionSource.Regex))]);

        var entities = composite.Detect("LN-456789");

        entities.Should().ContainSingle(entity =>
            entity.Type == PiiEntityType.LoanNumber &&
            entity.Source == PiiDetectionSource.Domain);
    }

    [Test]
    public void Detect_OverlappingPriority_RegexBeatsNer()
    {
        var composite = new CompositePiiDetector([new FixedDetector(
            new PiiEntity(PiiEntityType.Email, "a@b.co", 0, 6, PiiDetectionSource.Regex),
            new PiiEntity(PiiEntityType.Person, "a@b", 0, 3, PiiDetectionSource.Ner))]);

        var entities = composite.Detect("a@b.co");

        entities.Should().ContainSingle(entity => entity.Source == PiiDetectionSource.Regex);
    }

    [Test]
    public void Detect_OverlappingPriority_DomainBeatsNer()
    {
        var composite = new CompositePiiDetector([new FixedDetector(
            new PiiEntity(PiiEntityType.LoanNumber, "LN-456789", 0, 9, PiiDetectionSource.Domain),
            new PiiEntity(PiiEntityType.Person, "LN-456", 0, 6, PiiDetectionSource.Ner))]);

        var entities = composite.Detect("LN-456789");

        entities.Should().ContainSingle(entity => entity.Source == PiiDetectionSource.Domain);
    }

    [Test]
    public void Detect_DuplicateOverlappingSpan_KeepsFirstAccepted()
    {
        var composite = new CompositePiiDetector([new FixedDetector(
            new PiiEntity(PiiEntityType.Phone, "9876543210", 0, 10, PiiDetectionSource.Regex),
            new PiiEntity(PiiEntityType.Phone, "9876543210", 0, 10, PiiDetectionSource.Regex))]);

        var entities = composite.Detect("9876543210");

        entities.Should().HaveCount(1);
    }

    [Test]
    public void Detect_AadhaarWithEmbeddedPhone_PrefersAadhaarSpan()
    {
        var detector = new CompositePiiDetector(
        [
            new DomainRulePiiDetector(),
            new RegexPiiDetector()
        ]);

        var entities = detector.Detect("Aadhaar 987654321012 phone 9876543210.");

        entities.Should().Contain(entity => entity.Type == PiiEntityType.Aadhaar && entity.Value == "987654321012");
        entities.Should().Contain(entity => entity.Type == PiiEntityType.Phone && entity.Value == "9876543210");
        entities.Count(entity => entity.Type == PiiEntityType.Phone).Should().Be(1);
    }

    [TestCase(null)]
    [TestCase("")]
    [TestCase("   ")]
    public void Detect_InvalidInput_ThrowsArgumentException(string? text)
    {
        var composite = new CompositePiiDetector([new RegexPiiDetector()]);
        var action = () => composite.Detect(text!);
        action.Should().Throw<ArgumentException>();
    }

    private sealed class FixedDetector(params PiiEntity[] entities) : IPiiDetector
    {
        public IReadOnlyList<PiiEntity> Detect(string text) => entities;
    }
}