GameOverlay.Capture/tests/GameOverlay.Capture.Tests/FrameTimeTrackerTests.cs

using GameOverlay.Capture;
using Xunit;

namespace GameOverlay.Capture.Tests;

public class FrameTimeTrackerTests
{
    [Fact]
    public void FirstPresent_EstablishesBaseline_NoSample()
    {
        var tracker = new FrameTimeTracker();
        Assert.Null(tracker.AddPresent(1000.0));
        Assert.Equal(0, tracker.Count);
    }

    [Fact]
    public void SubsequentPresents_ProduceFrameTimeSamples()
    {
        var tracker = new FrameTimeTracker();
        tracker.AddPresent(0.0);
        var s1 = tracker.AddPresent(16.0);
        var s2 = tracker.AddPresent(32.0);

        Assert.NotNull(s1);
        Assert.Equal(16.0, s1!.Value.FrameTimeMs, 6);
        Assert.Equal(1000.0 / 16.0, s1.Value.Fps, 6);
        Assert.NotNull(s2);
        Assert.Equal(2, tracker.Count);
    }

    [Fact]
    public void OutOfOrderOrDuplicateTimestamps_AreIgnored()
    {
        var tracker = new FrameTimeTracker();
        tracker.AddPresent(100.0);
        Assert.Null(tracker.AddPresent(100.0)); // duplicate
        Assert.Null(tracker.AddPresent(90.0));  // out of order
        Assert.Equal(0, tracker.Count);
    }

    [Fact]
    public void Summary_ReflectsSteadyRate()
    {
        var tracker = new FrameTimeTracker();
        double t = 0;
        for (int i = 0; i < 101; i++) // 101 presents => 100 frame times of 10ms
        {
            tracker.AddPresent(t);
            t += 10.0;
        }

        var summary = tracker.ComputeSummary();
        Assert.Equal(100, summary.FrameCount);
        Assert.Equal(100.0, summary.AverageFps, 6);
    }

    [Fact]
    public void Reset_ClearsCountAndBaseline()
    {
        var tracker = new FrameTimeTracker();
        tracker.AddPresent(0);
        tracker.AddPresent(10);
        tracker.Reset();
        Assert.Equal(0, tracker.Count);
        Assert.Null(tracker.AddPresent(5)); // first after reset is a baseline again
    }
}