Make solution folders for warmup and integration

- Add OrderBookDomain: in-memory order book with Pending →
  WaitingForPayment → Fulfilling → Delivered state machine, payment
  window based on passed-in timestamps, cancellation rules
- Add OrderBookTests: 7 integration tests in given/when/then/when/then
  anti-pattern style as starting material for the exercise
- Learning hour: add round 2 where participants create the example
  themselves before showing it to the agent (no refactored test given)
- Fix sln: OrderTests Debug config was mapped to Release

exercises/show-dont-tell/.gitignore

@@ -17,3 +17,4 @@ obj/
 
 ## NuGet local config (workaround for locked ~/.nuget)
 nuget.config
+*.log

exercises/show-dont-tell/ShowDontTell.sln

@@ -6,6 +6,14 @@ Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "OrderDomain", "src/OrderDom
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "OrderTests", "tests/OrderTests/OrderTests.csproj", "{B2C3D4E5-F6A7-8901-BCDE-F12345678901}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "OrderBookDomain", "src/OrderBookDomain/OrderBookDomain.csproj", "{C3D4E5F6-A7B8-9012-CDEF-123456789012}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "OrderBookTests", "tests/OrderBookTests/OrderBookTests.csproj", "{D4E5F6A7-B8C9-0123-DEFA-234567890123}"
+EndProject
+Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Integration", "Integration", "{83A6B86A-4CD0-44BE-9FE0-408AC31E69F8}"
+EndProject
+Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Warmup", "Warmup", "{55470487-3CE4-4FD7-BADF-35F7D1473CA5}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -14,4 +22,24 @@ Global
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
 	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{A1B2C3D4-E5F6-7890-ABCD-EF1234567890}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{A1B2C3D4-E5F6-7890-ABCD-EF1234567890}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{A1B2C3D4-E5F6-7890-ABCD-EF1234567890}.Debug|Any CPU.Deploy.0 = Debug|Any CPU
+		{C3D4E5F6-A7B8-9012-CDEF-123456789012}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{C3D4E5F6-A7B8-9012-CDEF-123456789012}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{C3D4E5F6-A7B8-9012-CDEF-123456789012}.Debug|Any CPU.Deploy.0 = Debug|Any CPU
+		{D4E5F6A7-B8C9-0123-DEFA-234567890123}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{D4E5F6A7-B8C9-0123-DEFA-234567890123}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{D4E5F6A7-B8C9-0123-DEFA-234567890123}.Debug|Any CPU.Deploy.0 = Debug|Any CPU
+		{B2C3D4E5-F6A7-8901-BCDE-F12345678901}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{B2C3D4E5-F6A7-8901-BCDE-F12345678901}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{B2C3D4E5-F6A7-8901-BCDE-F12345678901}.Debug|Any CPU.Deploy.0 = Debug|Any CPU
+	EndGlobalSection
+	GlobalSection(NestedProjects) = preSolution
+		{C3D4E5F6-A7B8-9012-CDEF-123456789012} = {83A6B86A-4CD0-44BE-9FE0-408AC31E69F8}
+		{D4E5F6A7-B8C9-0123-DEFA-234567890123} = {83A6B86A-4CD0-44BE-9FE0-408AC31E69F8}
+		{A1B2C3D4-E5F6-7890-ABCD-EF1234567890} = {55470487-3CE4-4FD7-BADF-35F7D1473CA5}
+		{B2C3D4E5-F6A7-8901-BCDE-F12345678901} = {55470487-3CE4-4FD7-BADF-35F7D1473CA5}
+	EndGlobalSection
 EndGlobal

exercises/show-dont-tell/global.json

@@ -0,0 +1,6 @@
+{
+  "sdk": {
+    "version": "10.0.400",
+    "rollForward": "latestFeature"
+  }
+}

exercises/show-dont-tell/learning-hour.md

@@ -15,12 +15,14 @@ You've described what you want to a coding agent, and it didn't get it right. Or
 ## Learning Goals
 
 * Use a concrete code example (show, don't tell) to guide a coding agent in propagating a refactoring pattern across a test suite.
+* Produce your own example before delegating: refactor a multi-step test into focused tests yourself, then show the result to the agent as the pattern.
 
 ## Session Outline
 
 * 5 min connect: Frustrating agent conversations
 * 5 min concept: LLMs are pattern matchers
-* 35 min concrete practice: Refactor tests using a custom matcher example
+* 20 min concrete practice: Round 1 — refactor tests using a custom matcher example
+* 15 min concrete practice: Round 2 — split multi-step tests using an example you create
 * 5 min conclusion: Share back and recognize the pattern in your own code
 
 ## Connect — Frustrating Agent Conversations
@@ -80,7 +82,7 @@ The agent sees the concrete pattern and replicates it. No description needed.
 
 **Examples beat descriptions.** One concrete example is worth a paragraph of instructions. This works for any refactoring pattern — splitting tests, introducing custom matchers, extracting methods, renaming for clarity. Show the agent what "done" looks like.
 
-## Concrete Practice — Refactor Tests with a Custom Matcher
+## Concrete Practice — Round 1 — Refactor Tests with a Custom Matcher (20 min)
 
 ### Setup
 
@@ -136,6 +138,49 @@ Run the tests after the agent makes changes to verify nothing broke.
 - The `exercises/show-dont-tell/` project (included in this repo)
 - .NET 10 SDK
 
+## Concrete Practice — Round 2 — Split Multi-Step Tests (15 min)
+
+This round has a twist: **no refactored example is provided.** Creating the example is the exercise.
+
+### Setup
+
+In the same solution, open the `OrderBookTests` project. The domain is an `OrderBook` with a small state machine:
+
+* `OpenOrder(customer)` creates a `Pending` order
+* `FinalizeOrder(id, at)` → `WaitingForPayment` (the timestamp is passed in — no global clock)
+* `PayOrder(id, paidAt)` → `Fulfilling`, unless payment arrives more than 14 days after finalization: the order is `Cancelled` and the payment is rejected
+* `ShipOrder(id)` → `Delivered`
+* `CancelOrder(id)` works from `Pending` and `WaitingForPayment` only; invalid transitions throw
+
+`OrderBookLifecycleTests.cs` contains 7 integration tests in an anti-pattern style: **given/when/then/when/then**. Each test walks through several transitions with assertions in between, e.g. `PayThenShip_DeliversTheOrder` finalizes, asserts, pays, ships, and asserts again. The tests pass — they're just testing three behaviors each under a name that describes one.
+
+### Step 1 — Identify the Smell (3 min)
+
+Look at the tests. What makes them hard to work with?
+
+* Multiple act/assert pairs: when one assertion fails, you don't know which transition misbehaved
+* Test names describe one behavior while the test body verifies three
+* Setup for a later transition is entangled with assertions for an earlier one
+
+### Step 2 — Create the Example Yourself (7 min)
+
+Pick **one** multi-step test and refactor it by hand into focused tests: one transition per test, each test setting up only the state it needs. Keep the exception paths (`Assert.Throws`) in their own tests. Run the tests — the split versions must cover the same behavior as the original.
+
+You cannot show the agent what "done" looks like until you have built it. Notice what decisions you had to make: how to name the split tests, what setup helper to extract, where a transition deserves its own test.
+
+### Step 3 — Use Your Example with the Agent (5 min)
+
+Now show your refactored test to the agent and ask it to apply the same pattern to the remaining tests. Verify with the test run afterward.
+
+**If the agent doesn't get it right:**
+
+* Check whether your example is unambiguous — could it be read another way?
+* Compare with round 1: what did the provided example communicate that yours doesn't?
+
+### Why No Example Was Provided
+
+Round 1 showed that examples guide agents better than descriptions. Round 2 practices the harder half of that skill: producing the example. In real work, the pattern you want to propagate usually doesn't exist yet — someone has to write it first, and that someone is you.
+
 ## Conclusions — Share Back
 
 Go around and ask:
@@ -143,6 +188,7 @@ Go around and ask:
 1. **Did the agent get it right on the first try? What happened if it didn't?**
 2. **What made the example work — what would have made it fail?**
 3. **Do you recognize this pattern in your own tests?** Where could you use "show, don't tell" in your real work?
+4. **What was different in round 2, when you had to create the example yourself?** What made that harder — and what did you learn about writing a good example?
 
 This is an [Explain the Main Idea]({% link _activities/conclusions/explain_main_idea.md %}) conclusion.
 

exercises/show-dont-tell/mise.toml

@@ -0,0 +1,2 @@
+[tools]
+dotnet = "10"

exercises/show-dont-tell/src/OrderBookDomain/Order.cs

@@ -0,0 +1,25 @@
+namespace OrderBookDomain;
+
+public enum OrderStatus
+{
+    Pending,
+    WaitingForPayment,
+    Fulfilling,
+    Delivered,
+    Cancelled
+}
+
+public class Order
+{
+    public int Id { get; }
+    public string Customer { get; }
+    public OrderStatus Status { get; internal set; }
+    public DateTimeOffset? FinalizedAt { get; internal set; }
+
+    internal Order(int id, string customer)
+    {
+        Id = id;
+        Customer = customer;
+        Status = OrderStatus.Pending;
+    }
+}

exercises/show-dont-tell/src/OrderBookDomain/OrderBook.cs

@@ -0,0 +1,69 @@
+namespace OrderBookDomain;
+
+public class OrderBook
+{
+    private readonly TimeSpan _paymentWindow;
+    private readonly Dictionary<int, Order> _ordersById = new();
+    private int _nextId = 1;
+
+    public OrderBook(TimeSpan? paymentWindow = null)
+        => _paymentWindow = paymentWindow ?? TimeSpan.FromDays(14);
+
+    public IReadOnlyList<Order> Orders => _ordersById.Values.ToList();
+
+    public Order OpenOrder(string customer)
+    {
+        var order = new Order(_nextId++, customer);
+        _ordersById[order.Id] = order;
+        return order;
+    }
+
+    public Order GetOrder(int orderId)
+        => _ordersById.TryGetValue(orderId, out var order)
+            ? order
+            : throw new InvalidOperationException($"Unknown order id {orderId}.");
+
+    public void FinalizeOrder(int orderId, DateTimeOffset finalizedAt)
+    {
+        var order = GetOrder(orderId);
+        RequireStatus(order, OrderStatus.Pending, "finalize");
+        order.Status = OrderStatus.WaitingForPayment;
+        order.FinalizedAt = finalizedAt;
+    }
+
+    public void PayOrder(int orderId, DateTimeOffset paidAt)
+    {
+        var order = GetOrder(orderId);
+        RequireStatus(order, OrderStatus.WaitingForPayment, "pay");
+        if (paidAt - order.FinalizedAt > _paymentWindow)
+        {
+            order.Status = OrderStatus.Cancelled;
+            throw new InvalidOperationException(
+                $"Payment for order {orderId} arrived after the payment window; the order was cancelled.");
+        }
+        order.Status = OrderStatus.Fulfilling;
+    }
+
+    public void ShipOrder(int orderId)
+    {
+        var order = GetOrder(orderId);
+        RequireStatus(order, OrderStatus.Fulfilling, "ship");
+        order.Status = OrderStatus.Delivered;
+    }
+
+    public void CancelOrder(int orderId)
+    {
+        var order = GetOrder(orderId);
+        if (order.Status is not (OrderStatus.Pending or OrderStatus.WaitingForPayment))
+            throw new InvalidOperationException(
+                $"Cannot cancel order {orderId} in status {order.Status}.");
+        order.Status = OrderStatus.Cancelled;
+    }
+
+    private static void RequireStatus(Order order, OrderStatus expected, string action)
+    {
+        if (order.Status != expected)
+            throw new InvalidOperationException(
+                $"Cannot {action} order {order.Id} in status {order.Status} (expected {expected}).");
+    }
+}

exercises/show-dont-tell/src/OrderBookDomain/OrderBookDomain.csproj

@@ -0,0 +1,7 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+</Project>

exercises/show-dont-tell/tests/OrderBookTests/OrderBookLifecycleTests.cs

@@ -0,0 +1,114 @@
+using NUnit.Framework;
+using OrderBookDomain;
+
+namespace OrderBookTests;
+
+public class OrderBookLifecycleTests
+{
+    private static readonly DateTimeOffset Day0 = new(2025, 6, 1, 0, 0, 0, TimeSpan.Zero);
+
+    private static DateTimeOffset At(int day) => Day0.AddDays(day);
+
+    [Test]
+    public void FinalizeThenPay_MovesOrderThroughTwoStates()
+    {
+        var book = new OrderBook();
+        var order = book.OpenOrder("anna");
+
+        book.FinalizeOrder(order.Id, At(1));
+        Assert.That(book.GetOrder(order.Id).Status, Is.EqualTo(OrderStatus.WaitingForPayment));
+
+        book.PayOrder(order.Id, At(2));
+        Assert.That(book.GetOrder(order.Id).Status, Is.EqualTo(OrderStatus.Fulfilling));
+    }
+
+    [Test]
+    public void PayThenShip_DeliversTheOrder()
+    {
+        var book = new OrderBook();
+        var order = book.OpenOrder("anna");
+
+        book.FinalizeOrder(order.Id, At(1));
+        Assert.That(book.GetOrder(order.Id).Status, Is.EqualTo(OrderStatus.WaitingForPayment));
+
+        book.PayOrder(order.Id, At(2));
+        book.ShipOrder(order.Id);
+        Assert.That(book.GetOrder(order.Id).Status, Is.EqualTo(OrderStatus.Delivered));
+    }
+
+    [Test]
+    public void PayWithinWindow_ThenLatePayOnSecondOrder_CancelsOnlyThatOrder()
+    {
+        var book = new OrderBook();
+        var first = book.OpenOrder("anna");
+        var second = book.OpenOrder("bram");
+
+        book.FinalizeOrder(first.Id, At(1));
+        book.FinalizeOrder(second.Id, At(1));
+        Assert.That(book.Orders, Has.Count.EqualTo(2));
+
+        book.PayOrder(first.Id, At(5));
+        Assert.That(book.GetOrder(first.Id).Status, Is.EqualTo(OrderStatus.Fulfilling));
+
+        Assert.Throws<InvalidOperationException>(() => book.PayOrder(second.Id, At(30)));
+        Assert.That(book.GetOrder(second.Id).Status, Is.EqualTo(OrderStatus.Cancelled));
+    }
+
+    [Test]
+    public void PayBeforeFinalize_Throws_ThenFinalizeStillWorks()
+    {
+        var book = new OrderBook();
+        var order = book.OpenOrder("anna");
+
+        Assert.Throws<InvalidOperationException>(() => book.PayOrder(order.Id, At(1)));
+        Assert.That(book.GetOrder(order.Id).Status, Is.EqualTo(OrderStatus.Pending));
+
+        book.FinalizeOrder(order.Id, At(2));
+        Assert.That(book.GetOrder(order.Id).Status, Is.EqualTo(OrderStatus.WaitingForPayment));
+    }
+
+    [Test]
+    public void CancelPendingOrder_ThenPayAfterCancel_ThrowsAgain()
+    {
+        var book = new OrderBook();
+        var order = book.OpenOrder("anna");
+
+        book.CancelOrder(order.Id);
+        Assert.That(book.GetOrder(order.Id).Status, Is.EqualTo(OrderStatus.Cancelled));
+
+        Assert.Throws<InvalidOperationException>(() => book.PayOrder(order.Id, At(1)));
+        Assert.That(book.GetOrder(order.Id).Status, Is.EqualTo(OrderStatus.Cancelled));
+    }
+
+    [Test]
+    public void ShippedOrder_CannotBeCancelled()
+    {
+        var book = new OrderBook();
+        var order = book.OpenOrder("anna");
+
+        book.FinalizeOrder(order.Id, At(1));
+        book.PayOrder(order.Id, At(2));
+        book.ShipOrder(order.Id);
+        Assert.That(book.GetOrder(order.Id).Status, Is.EqualTo(OrderStatus.Delivered));
+
+        Assert.Throws<InvalidOperationException>(() => book.CancelOrder(order.Id));
+        Assert.That(book.GetOrder(order.Id).Status, Is.EqualTo(OrderStatus.Delivered));
+    }
+
+    [Test]
+    public void TwoCustomers_InterleaveTransitions_Independently()
+    {
+        var book = new OrderBook();
+        var annas = book.OpenOrder("anna");
+        var brams = book.OpenOrder("bram");
+
+        book.FinalizeOrder(brams.Id, At(1));
+        Assert.That(book.GetOrder(annas.Id).Status, Is.EqualTo(OrderStatus.Pending));
+        Assert.That(book.GetOrder(brams.Id).Status, Is.EqualTo(OrderStatus.WaitingForPayment));
+
+        book.PayOrder(brams.Id, At(2));
+        book.CancelOrder(annas.Id);
+        Assert.That(book.GetOrder(annas.Id).Status, Is.EqualTo(OrderStatus.Cancelled));
+        Assert.That(book.GetOrder(brams.Id).Status, Is.EqualTo(OrderStatus.Fulfilling));
+    }
+}

exercises/show-dont-tell/tests/OrderBookTests/OrderBookTests.csproj

@@ -0,0 +1,16 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+    <IsTestProject>true</IsTestProject>
+  </PropertyGroup>
+  <ItemGroup>
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
+    <PackageReference Include="NUnit" Version="4.6.1" />
+    <PackageReference Include="NUnit3TestAdapter" Version="6.3.0" />
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\..\src\OrderBookDomain\OrderBookDomain.csproj" />
+  </ItemGroup>
+</Project>

exercises/show-dont-tell/tests/OrderTests/OrderStateConstraint.cs

@@ -12,9 +12,7 @@ namespace OrderTests;
 public static class Has
 {
     public static IResolveConstraint OrderState(decimal expectedTotal, decimal[] expectedLineValues)
-    {
+        => new OrderStateConstraint(expectedTotal, expectedLineValues);
-        return new OrderStateConstraint(expectedTotal, expectedLineValues);
-    }
 }
 
 public class OrderStateConstraint : Constraint
@@ -23,27 +21,54 @@ public class OrderStateConstraint : Constraint
     private readonly decimal[] _expectedLineValues;
 
     public OrderStateConstraint(decimal expectedTotal, decimal[] expectedLineValues)
-        : base($"order with total {expectedTotal} and line values [{string.Join(", ", expectedLineValues)}]")
     {
         _expectedTotal = expectedTotal;
         _expectedLineValues = expectedLineValues;
     }
 
+    public override string Description =>
+        $"order with total {_expectedTotal} and line values [{string.Join(", ", _expectedLineValues)}]";
+
     public override ConstraintResult ApplyTo<TActual>(TActual actual)
     {
         var order = (Order)(object)actual!;
         var actualTotal = order.Total;
         var actualLineValues = order.Lines.Select(l => l.Value).ToArray();
 
-        var totalMatch = actualTotal == _expectedTotal;
+        var details = new List<string>();
-        var linesMatch = actualLineValues.SequenceEqual(_expectedLineValues);
+        if (actualTotal != _expectedTotal)
+            details.Add($"Total: expected {_expectedTotal}, but was {actualTotal}");
+        if (!actualLineValues.SequenceEqual(_expectedLineValues))
+            details.Add(
+                $"Line values: expected [{string.Join(", ", _expectedLineValues)}], " +
+                $"but was [{string.Join(", ", actualLineValues)}]");
 
-        var messages = new List<string>();
+        return new OrderStateResult(this, actual!, details.Count == 0, details);
-        if (!totalMatch)
-            messages.Add($"Total: expected {_expectedTotal}, got {actualTotal}");
-        if (!linesMatch)
-            messages.Add($"Line values: expected [{string.Join(", ", _expectedLineValues)}], got [{string.Join(", ", actualLineValues)}]");
-
-        return new ConstraintResult(this, actual, totalMatch && linesMatch);
     }
-}
+
+    /// <summary>
+    /// A ConstraintResult that carries the per-field mismatch details and
+    /// writes them as additional lines in the failure message, e.g.
+    ///
+    ///   Expected: order with total 210 and line values [160, 50]
+    ///   But was:  &lt;Order&gt;
+    ///     Total: expected 210, but was 250
+    ///     Line values: expected [160, 50], but was [200, 50]
+    /// </summary>
+    private sealed class OrderStateResult : ConstraintResult
+    {
+        private readonly IReadOnlyList<string> _details;
+
+        public OrderStateResult(Constraint constraint, object? actual, bool isSuccess, IReadOnlyList<string> details)
+            : base(constraint, actual, isSuccess)
+        {
+            _details = details;
+        }
+
+        public override void WriteAdditionalLinesTo(MessageWriter writer)
+        {
+            foreach (var detail in _details)
+                writer.WriteMessageLine(detail);
+        }
+    }
+}

exercises/show-dont-tell/tests/OrderTests/OrderTests.csproj

@@ -7,8 +7,8 @@
   </PropertyGroup>
   <ItemGroup>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
-    <PackageReference Include="NUnit" Version="3.13.3" />
+    <PackageReference Include="NUnit" Version="4.6.1" />
-    <PackageReference Include="NUnit3TestAdapter" Version="4.6.0" />
+    <PackageReference Include="NUnit3TestAdapter" Version="6.3.0" />
   </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="..\..\src\OrderDomain\OrderDomain.csproj" />

exercises/show-dont-tell/tests/OrderTests/OrderTotalTests.cs

@@ -18,7 +18,7 @@ public class OrderTotalTests
 
         Assert.That(order, Has.OrderState(
             expectedTotal: 210m,
-            expectedLineValues: new[] { 160m, 50m }));
+             expectedLineValues: [160m, 50m]));
     }
 
     [Test]