Build flashsharp flashcard app

tests/Flashsharp.Tests/SchedulerTests.cs

@@ -0,0 +1,77 @@
+using Flashsharp.Domain;
+using Flashsharp.Scheduling;
+
+namespace Flashsharp.Tests;
+
+public sealed class SchedulerTests
+{
+    static readonly DateTime Now = new(2026, 10, 22, 12, 0, 0, DateTimeKind.Utc);
+
+    [Fact]
+    public void First_good_review_is_due_tomorrow()
+    {
+        var next = Scheduler.Next(null, ReviewRating.Good, Now);
+
+        Assert.Equal(86_400, next.IntervalSeconds);
+        Assert.Equal(1, next.Repetitions);
+        Assert.Equal(0, next.Lapses);
+        Assert.Equal(2.5, next.Ease, 3);
+        Assert.Equal(Now.AddDays(1), next.DueAt);
+    }
+
+    [Fact]
+    public void Third_good_review_multiplies_by_ease()
+    {
+        var first = Scheduler.Next(null, ReviewRating.Good, Now);
+        var second = Scheduler.Next(first, ReviewRating.Good, Now);
+        var third = Scheduler.Next(second, ReviewRating.Good, Now);
+
+        Assert.Equal(3 * 86_400, second.IntervalSeconds);
+        Assert.Equal((int)(3 * 86_400 * 2.5), third.IntervalSeconds);
+        Assert.Equal(3, third.Repetitions);
+    }
+
+    [Fact]
+    public void Again_resets_repetitions_and_adds_a_lapse()
+    {
+        var first = Scheduler.Next(null, ReviewRating.Good, Now);
+        var next = Scheduler.Next(first, ReviewRating.Again, Now);
+
+        Assert.Equal(600, next.IntervalSeconds);
+        Assert.Equal(0, next.Repetitions);
+        Assert.Equal(1, next.Lapses);
+        Assert.Equal(2.3, next.Ease, 3);
+    }
+
+    [Fact]
+    public void Hard_does_not_reset_repetitions()
+    {
+        var first = Scheduler.Next(null, ReviewRating.Good, Now);
+        var next = Scheduler.Next(first, ReviewRating.Hard, Now);
+
+        Assert.Equal(2, next.Repetitions);
+        Assert.Equal(0, next.Lapses);
+        Assert.True(next.IntervalSeconds >= 43_200);
+    }
+
+    [Fact]
+    public void Easy_starts_at_three_days_and_raises_ease()
+    {
+        var next = Scheduler.Next(null, ReviewRating.Easy, Now);
+
+        Assert.Equal(3 * 86_400, next.IntervalSeconds);
+        Assert.Equal(2.65, next.Ease, 3);
+    }
+
+    [Fact]
+    public void Ease_never_goes_below_floor()
+    {
+        var state = Scheduler.Next(null, ReviewRating.Again, Now);
+        for (var i = 0; i < 20; i++)
+        {
+            state = Scheduler.Next(state, ReviewRating.Again, Now);
+        }
+
+        Assert.Equal(1.3, state.Ease, 3);
+    }
+}