4 files changed, 105 insertions, 0 deletions
diff --git a/tests/Agent.Planner.Tests/Agent.Planner.Tests.csproj b/tests/Agent.Planner.Tests/Agent.Planner.Tests.csproj
new file mode 100644
index 0000000..16264cb
--- /dev/null
+++ b/tests/Agent.Planner.Tests/Agent.Planner.Tests.csproj
@@ -0,0 +1,14 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <IsPackable>false</IsPackable>
+    <IsTestProject>true</IsTestProject>
+    <TestingPlatformDotnetTestSupport>true</TestingPlatformDotnetTestSupport>
+  </PropertyGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\..\src\Agent.Planner\Agent.Planner.csproj" />
+  </ItemGroup>
+  <ItemGroup>
+    <PackageReference Include="Microsoft.NET.Test.Sdk" />
+    <PackageReference Include="xunit.v3" />
+  </ItemGroup>
+</Project>
diff --git a/tests/Agent.Planner.Tests/BaselineTests.cs b/tests/Agent.Planner.Tests/BaselineTests.cs
new file mode 100644
index 0000000..a459b18
--- /dev/null
+++ b/tests/Agent.Planner.Tests/BaselineTests.cs
@@ -0,0 +1,10 @@
+namespace Agent.Planner.Tests;
+
+public sealed class BaselineTests
+{
+    [Fact]
+    public void PlannerAssemblyLoads()
+    {
+        Assert.Equal("Agent.Planner", typeof(Planner.AssemblyMarker).Assembly.GetName().Name);
+    }
+}
diff --git a/tests/Agent.Planner.Tests/TaskGraphTests.cs b/tests/Agent.Planner.Tests/TaskGraphTests.cs
new file mode 100644
index 0000000..b09cd56
--- /dev/null
+++ b/tests/Agent.Planner.Tests/TaskGraphTests.cs
@@ -0,0 +1,80 @@
+using Agent.Planner;
+
+namespace Agent.Planner.Tests;
+
+public sealed class TaskGraphTests
+{
+    private static readonly TokenEstimate Small = new(60, 60, 60);
+
+    [Fact]
+    public void Known_dag_has_deterministic_critical_path()
+    {
+        TaskGraph graph = new();
+        PlannerTask a = graph.AddTask("A", TokenBudgetClass.K1, new TokenEstimate(60, 60, 60));
+        PlannerTask b = graph.AddTask("B", TokenBudgetClass.K1, new TokenEstimate(120, 120, 120), [a.Id]);
+        _ = graph.AddTask("C", TokenBudgetClass.K1, new TokenEstimate(30, 30, 30), [a.Id]);
+        PlannerTask d = graph.AddTask("D", TokenBudgetClass.K1, new TokenEstimate(60, 60, 60), [b.Id]);
+
+        Assert.Equal([a.Id, b.Id, d.Id], graph.CriticalPath.TaskIds);
+        Assert.Equal(240, graph.CriticalPath.CumulativeTokenCost);
+    }
+
+    [Fact]
+    public void Cycle_is_rejected_without_mutating_graph()
+    {
+        TaskGraph graph = new();
+        PlannerTask a = graph.AddTask("A", TokenBudgetClass.K1, Small);
+        PlannerTask b = graph.AddTask("B", TokenBudgetClass.K1, Small, [a.Id]);
+
+        Assert.Throws<PlannerValidationException>(() => graph.AddDependency(a.Id, b.Id));
+        Assert.Empty(graph.Get(a.Id).Dependencies);
+    }
+
+    [Fact]
+    public void Max_tasks_is_enforced()
+    {
+        TaskGraph graph = new(1);
+        _ = graph.AddTask("A", TokenBudgetClass.K1, Small);
+        Assert.Throws<PlannerValidationException>(() => graph.AddTask("B", TokenBudgetClass.K1, Small));
+    }
+
+    [Theory]
+    [InlineData(0, 1, 1)]
+    [InlineData(2, 1, 2)]
+    [InlineData(1, 3, 2)]
+    [InlineData(1, 2, 2048)]
+    public void Invalid_estimate_is_rejected(long optimistic, long likely, long pessimistic)
+    {
+        TaskGraph graph = new();
+        Assert.Throws<PlannerValidationException>(() => graph.AddTask("bad", TokenBudgetClass.K1, new TokenEstimate(optimistic, likely, pessimistic)));
+    }
+
+    [Fact]
+    public void Completed_task_is_immutable()
+    {
+        TaskGraph graph = new();
+        PlannerTask task = graph.AddTask("A", TokenBudgetClass.K1, Small);
+        graph.SetState(task.Id, PlannerTaskState.Completed);
+
+        Assert.Throws<PlannerValidationException>(() => graph.SetEstimate(task.Id, TokenBudgetClass.K2, new TokenEstimate(1, 2, 3)));
+        Assert.Throws<PlannerValidationException>(() => graph.SetState(task.Id, PlannerTaskState.Failed));
+        Assert.Throws<PlannerValidationException>(() => graph.AddUsage(task.Id, 1, 1));
+    }
+
+    [Fact]
+    public void Graph_change_recalculates_cpm_and_usage_accumulates()
+    {
+        TaskGraph graph = new();
+        PlannerTask a = graph.AddTask("A", TokenBudgetClass.K1, Small);
+        PlannerTask b = graph.AddTask("B", TokenBudgetClass.K1, new TokenEstimate(30, 30, 30));
+        Assert.Equal([a.Id], graph.CriticalPath.TaskIds);
+
+        graph.AddDependency(b.Id, a.Id);
+        graph.AddUsage(b.Id, 10, 5);
+        graph.AddUsage(b.Id, 2, 3);
+
+        Assert.Equal([a.Id, b.Id], graph.CriticalPath.TaskIds);
+        Assert.Equal(20, graph.Get(b.Id).ActualTotalTokens);
+        Assert.Equal(2_048, graph.TotalTokenBudget);
+    }
+}
diff --git a/tests/Agent.Planner.Tests/Usings.cs b/tests/Agent.Planner.Tests/Usings.cs
new file mode 100644
index 0000000..c802f44
--- /dev/null
+++ b/tests/Agent.Planner.Tests/Usings.cs
@@ -0,0 +1 @@
+global using Xunit;