add test project

csharp-fp2.Tests/AccountTests.cs

@@ -0,0 +1,51 @@
+using CsharpFp2.Domain;
+
+namespace CsharpFp2.Tests;
+
+/// Tests covering domain-layer invariants on the Account aggregate directly,
+/// independent of the application layer.
+public class AccountTests
+{
+    [Fact]
+    public void Opening_an_account_with_a_negative_balance_throws()
+    {
+        Assert.Throws<ArgumentOutOfRangeException>(() =>
+            new Account(new AccountId(Guid.NewGuid()), new Money(-1m))
+        );
+    }
+
+    [Fact]
+    public void Withdrawing_a_zero_amount_throws()
+    {
+        var account = new Account(new AccountId(Guid.NewGuid()), new Money(100m));
+
+        Assert.Throws<InvalidOperationException>(() => account.Withdraw(new Money(0m)));
+    }
+
+    [Fact]
+    public void Withdrawing_a_negative_amount_throws()
+    {
+        var account = new Account(new AccountId(Guid.NewGuid()), new Money(100m));
+
+        Assert.Throws<InvalidOperationException>(() => account.Withdraw(new Money(-10m)));
+    }
+
+    [Fact]
+    public void Withdrawing_more_than_the_balance_throws()
+    {
+        var account = new Account(new AccountId(Guid.NewGuid()), new Money(100m));
+
+        Assert.Throws<InsufficientBalanceException>(() => account.Withdraw(new Money(101m)));
+    }
+
+    [Fact]
+    public void Successive_withdrawals_are_each_applied_to_the_running_balance()
+    {
+        var account = new Account(new AccountId(Guid.NewGuid()), new Money(300m));
+
+        account.Withdraw(new Money(100m));
+        account.Withdraw(new Money(100m));
+
+        Assert.Equal(100m, account.Balance.Amount);
+    }
+}

csharp-fp2.Tests/WithdrawMoneyHandlerTests.cs

@@ -0,0 +1,85 @@
+using CsharpFp2.Applications;
+using CsharpFp2.Contracts;
+using CsharpFp2.Domain;
+using CsharpFp2.Infrastructure;
+
+namespace CsharpFp2.Tests;
+
+/// Tests covering the application-layer use case surface:
+/// what the WithdrawMoney feature does from the caller's perspective.
+public class WithdrawMoneyHandlerTests
+{
+    private static (
+        WithdrawMoneyHandler handler,
+        InMemoryAccountRepository repository
+    ) BuildHandler()
+    {
+        var repository = new InMemoryAccountRepository();
+        var handler = new WithdrawMoneyHandler(repository);
+        return (handler, repository);
+    }
+
+    [Fact]
+    public void Withdrawing_from_an_account_reduces_its_balance_by_the_withdrawn_amount()
+    {
+        var (handler, repository) = BuildHandler();
+        var accountId = Guid.NewGuid();
+        repository.Save(new Account(new AccountId(accountId), new Money(200m)));
+
+        handler.Handle(new WithdrawMoneyCommand { AccountId = accountId, Amount = 75m });
+
+        var account = repository.GetById(new AccountId(accountId))!;
+        Assert.Equal(125m, account.Balance.Amount);
+    }
+
+    [Fact]
+    public void Withdrawing_the_entire_balance_leaves_the_account_at_zero()
+    {
+        var (handler, repository) = BuildHandler();
+        var accountId = Guid.NewGuid();
+        repository.Save(new Account(new AccountId(accountId), new Money(100m)));
+
+        handler.Handle(new WithdrawMoneyCommand { AccountId = accountId, Amount = 100m });
+
+        var account = repository.GetById(new AccountId(accountId))!;
+        Assert.Equal(0m, account.Balance.Amount);
+    }
+
+    [Fact]
+    public void Withdrawing_from_a_non_existent_account_throws()
+    {
+        var (handler, _) = BuildHandler();
+        var command = new WithdrawMoneyCommand { AccountId = Guid.NewGuid(), Amount = 50m };
+
+        Assert.Throws<InvalidOperationException>(() => handler.Handle(command));
+    }
+
+    [Fact]
+    public void Withdrawing_more_than_the_available_balance_throws()
+    {
+        var (handler, repository) = BuildHandler();
+        var accountId = Guid.NewGuid();
+        repository.Save(new Account(new AccountId(accountId), new Money(50m)));
+
+        Assert.Throws<InsufficientBalanceException>(() =>
+            handler.Handle(new WithdrawMoneyCommand { AccountId = accountId, Amount = 100m })
+        );
+    }
+
+    [Fact]
+    public void After_a_failed_withdrawal_the_balance_is_unchanged()
+    {
+        var (handler, repository) = BuildHandler();
+        var accountId = Guid.NewGuid();
+        repository.Save(new Account(new AccountId(accountId), new Money(50m)));
+
+        try
+        {
+            handler.Handle(new WithdrawMoneyCommand { AccountId = accountId, Amount = 999m });
+        }
+        catch (InsufficientBalanceException) { }
+
+        var account = repository.GetById(new AccountId(accountId))!;
+        Assert.Equal(50m, account.Balance.Amount);
+    }
+}

csharp-fp2.Tests/csharp-fp2.Tests.csproj

@@ -0,0 +1,26 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <RootNamespace>CsharpFp2.Tests</RootNamespace>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+    <IsPackable>false</IsPackable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="coverlet.collector" Version="6.0.4" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.14.1" />
+    <PackageReference Include="xunit" Version="2.9.3" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="3.1.4" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <Using Include="Xunit" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\csharp-fp2\csharp-fp2.csproj" />
+  </ItemGroup>
+
+</Project>

csharp.sln

@@ -19,6 +19,8 @@ Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "csharp-fp1", "csharp-fp1\cs
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "csharp-fp2", "csharp-fp2\csharp-fp2.csproj", "{10A6FD3E-117A-4C9E-98E2-DAC31E7CE78A}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "csharp-fp2.Tests", "csharp-fp2.Tests\csharp-fp2.Tests.csproj", "{4AFF063B-7125-4783-BE84-E1E9B4E2A462}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -101,6 +103,18 @@ Global
 		{10A6FD3E-117A-4C9E-98E2-DAC31E7CE78A}.Release|x64.Build.0 = Release|Any CPU
 		{10A6FD3E-117A-4C9E-98E2-DAC31E7CE78A}.Release|x86.ActiveCfg = Release|Any CPU
 		{10A6FD3E-117A-4C9E-98E2-DAC31E7CE78A}.Release|x86.Build.0 = Release|Any CPU
+		{4AFF063B-7125-4783-BE84-E1E9B4E2A462}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{4AFF063B-7125-4783-BE84-E1E9B4E2A462}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{4AFF063B-7125-4783-BE84-E1E9B4E2A462}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{4AFF063B-7125-4783-BE84-E1E9B4E2A462}.Debug|x64.Build.0 = Debug|Any CPU
+		{4AFF063B-7125-4783-BE84-E1E9B4E2A462}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{4AFF063B-7125-4783-BE84-E1E9B4E2A462}.Debug|x86.Build.0 = Debug|Any CPU
+		{4AFF063B-7125-4783-BE84-E1E9B4E2A462}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{4AFF063B-7125-4783-BE84-E1E9B4E2A462}.Release|Any CPU.Build.0 = Release|Any CPU
+		{4AFF063B-7125-4783-BE84-E1E9B4E2A462}.Release|x64.ActiveCfg = Release|Any CPU
+		{4AFF063B-7125-4783-BE84-E1E9B4E2A462}.Release|x64.Build.0 = Release|Any CPU
+		{4AFF063B-7125-4783-BE84-E1E9B4E2A462}.Release|x86.ActiveCfg = Release|Any CPU
+		{4AFF063B-7125-4783-BE84-E1E9B4E2A462}.Release|x86.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
@@ -112,5 +126,6 @@ Global
 		{7237398A-2E8B-4161-BA15-DB090395A1F2} = {CEC0EC27-0CEC-90C6-CABA-E58AB278E4DA}
 		{C9D46510-994A-4C43-BA8F-33CA9BED79D0} = {89C53051-77F9-4C1C-ABE5-6D54AB398471}
 		{10A6FD3E-117A-4C9E-98E2-DAC31E7CE78A} = {89C53051-77F9-4C1C-ABE5-6D54AB398471}
+		{4AFF063B-7125-4783-BE84-E1E9B4E2A462} = {89C53051-77F9-4C1C-ABE5-6D54AB398471}
 	EndGlobalSection
 EndGlobal