docs(architecture): ADR-0004 — Reqnroll as BDD framework (refs #5)

Record the choice of Reqnroll.xUnit for the acceptance layer introduced in
S-04, and register the previously-unlisted ADR-0002/0003 in the MkDocs nav.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.gitignore

@@ -5,6 +5,9 @@ obj/
 [Rr]elease/
 *.user
 
+# Reqnroll-generated test code (regenerated from *.feature on build)
+*.feature.cs
+
 # Test results / coverage
 [Tt]est[Rr]esults/
 *.trx

docs/architecture/adr-0004-bdd-framework.md

@@ -0,0 +1,52 @@
+# ADR-0004: Reqnroll as the BDD acceptance framework
+
+- **Status:** Accepted
+- **Date:** 2026-06-04
+- **Deciders:** Respellion engineering
+- **Relates to:** S-04 (#5); supports CLAUDE.md §3 (BDD at the use-case level) and §11 (tests pyramid)
+
+## Context
+
+CLAUDE.md §11 mandates that each user-visible flow is driven by a Gherkin acceptance
+scenario living in `tests/acceptance/`, and §3 names "BDD at the use-case level" as a core
+engineering principle. The foundational slices (S-00…S-03) added no acceptance layer; S-04
+is the first slice with real domain behaviour to drive, so it is where the BDD framework is
+introduced. We need a .NET tool that:
+
+- parses Gherkin `.feature` files and binds steps to C#,
+- integrates with the existing xUnit test runner (the repo standardises on xUnit), so
+  acceptance tests run under the same `dotnet test` / `make ci` gate as everything else,
+- is actively maintained on modern .NET (we target net10.0).
+
+## Decision
+
+**Use [Reqnroll](https://reqnroll.net/) (`Reqnroll.xUnit`) for acceptance tests.**
+
+- Reqnroll is the actively-maintained, open-source successor to SpecFlow (which is no longer
+  maintained). It keeps the same Gherkin + `[Binding]` model, so the knowledge transfers.
+- `Reqnroll.xUnit` generates one xUnit test per scenario, so acceptance tests are discovered
+  and run by the same runner as the unit tests — no second test framework, no extra CI step.
+- Acceptance projects live under `tests/acceptance/` per the PRD §9 layout. Generated
+  `*.feature.cs` files are build artefacts and are git-ignored.
+
+## Consequences
+
+- **Positive:** one assertion/runner stack (xUnit) across unit and acceptance tests; scenarios
+  are written in business language (Dutch domain terms inline) and reviewed as the slice's
+  contract; maintained tooling on net10.0.
+- **Cost:** a new dependency (`Reqnroll.xUnit`) and its xUnit v2 transitive graph. Reqnroll
+  pulls `xunit.core` but not the assertion library, so the `xunit` metapackage is referenced
+  explicitly to get `Assert`.
+- **Replaceable by:** hand-written xUnit "scenario" tests with a Given/When/Then helper, at
+  the cost of losing Gherkin as the shared, readable contract — which is the whole point of §3.
+- **Follow-ups:** the real-OpenZaak integration test (Testcontainers) and the Stryker mutation
+  baseline for S-04 are tracked as their own issues split off #5.
+
+## Alternatives considered
+
+- **SpecFlow** — rejected: unmaintained and without an official net10.0 story; Reqnroll is its
+  drop-in successor.
+- **Plain xUnit Given/When/Then helpers** — rejected for user-visible flows: loses the
+  business-readable Gherkin contract that §3/§11 require. Still fine for unit-level tests.
+- **Xunit.Gherkin.Quick** — rejected: lighter but less featureful (no hooks/scoped contexts,
+  smaller community) than Reqnroll.

mkdocs.yml

@@ -23,6 +23,9 @@ nav:
   - Product Requirements: PRD.md
   - Architecture:
       - "ADR-0001: Loose coupling": architecture/adr-0001-loose-coupling.md
+      - "ADR-0002: Catalogus design": architecture/adr-0002-catalogus-design.md
+      - "ADR-0003: ACL default-fill": architecture/adr-0003-default-fill.md
+      - "ADR-0004: BDD framework": architecture/adr-0004-bdd-framework.md
   - Working in Gitea: gitea-workflow.md
   - Runbooks:
       - CI: runbooks/ci.md

register-referentie.slnx

@@ -10,4 +10,7 @@
     <Project Path="services/bff/Bff.Api/Bff.Api.csproj" />
     <Project Path="services/bff/Bff.Tests/Bff.Tests.csproj" />
   </Folder>
+  <Folder Name="/tests/">
+    <Project Path="tests/acceptance/Acceptance.csproj" />
+  </Folder>
 </Solution>

tests/acceptance/Acceptance.csproj

@@ -0,0 +1,23 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <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="Reqnroll.xUnit" Version="3.3.4" />
+    <PackageReference Include="xunit" Version="2.9.3" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="3.1.4" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\services\acl\Acl.Application\Acl.Application.csproj" />
+    <ProjectReference Include="..\..\services\acl\Acl.Infrastructure\Acl.Infrastructure.csproj" />
+  </ItemGroup>
+
+</Project>

tests/acceptance/Features/EenZaakOpenen.feature

@@ -0,0 +1,27 @@
+# language: en
+# Drives S-04 (#5). The ACL is the only code that talks to ZGW (ADR-0001); it
+# default-fills the ZGW-mandatory zaak fields the domain never sees (ADR-0003).
+# Real-OpenZaak verification is a separate slice — this scenario exercises the
+# use case against an in-memory stand-in for the Zaken API.
+Feature: Een zaak openen vanuit een registratie
+  Als domein wil ik de ACL vragen een zaak te openen
+  zodat de ZGW-verplichte velden worden ingevuld zonder dat het domein ze kent.
+
+  Scenario: De ACL vult de ZGW-verplichte velden default in
+    Given a domain registration for BSN "123456782"
+    And the ACL is configured with these defaults:
+      | field                        | value                                         |
+      | bronorganisatie              | 517439943                                     |
+      | verantwoordelijkeOrganisatie | 517439943                                     |
+      | vertrouwelijkheidaanduiding  | openbaar                                      |
+      | zaaktype                     | http://openzaak/catalogi/api/v1/zaaktypen/big |
+    And today is "2026-06-04"
+    When the domain asks the ACL to open a zaak
+    Then a zaak is created with these default-filled fields
+      | field                        | value                                         |
+      | bronorganisatie              | 517439943                                     |
+      | verantwoordelijkeOrganisatie | 517439943                                     |
+      | vertrouwelijkheidaanduiding  | openbaar                                      |
+      | zaaktype                     | http://openzaak/catalogi/api/v1/zaaktypen/big |
+      | startdatum                   | 2026-06-04                                    |
+    And the ACL returns the URL of the created zaak

tests/acceptance/Steps/EenZaakOpenenSteps.cs

@@ -0,0 +1,65 @@
+using Acceptance.Support;
+using Acl.Application;
+using Reqnroll;
+using Xunit;
+
+namespace Acceptance.Steps;
+
+/// <summary>Bindings for <c>EenZaakOpenen.feature</c>. Reqnroll creates one
+/// instance per scenario, so instance fields hold scenario-scoped state.</summary>
+[Binding]
+public sealed class EenZaakOpenenSteps
+{
+    private readonly InMemoryZaakGateway _gateway = new();
+    private DomainRegistration? _registration;
+    private AclDefaults? _defaults;
+    private DateOnly _today;
+    private Uri? _returnedUrl;
+
+    [Given("a domain registration for BSN \"(.*)\"")]
+    public void GivenADomainRegistrationForBsn(string bsn)
+        => _registration = new DomainRegistration(bsn);
+
+    [Given("the ACL is configured with these defaults:")]
+    public void GivenTheAclIsConfiguredWithTheseDefaults(DataTable defaults)
+    {
+        var values = ToFieldMap(defaults);
+        _defaults = new AclDefaults
+        {
+            Bronorganisatie = values["bronorganisatie"],
+            VerantwoordelijkeOrganisatie = values["verantwoordelijkeOrganisatie"],
+            Vertrouwelijkheidaanduiding = values["vertrouwelijkheidaanduiding"],
+            ZaaktypeUrl = new Uri(values["zaaktype"]),
+        };
+    }
+
+    [Given("today is \"(.*)\"")]
+    public void GivenTodayIs(string date)
+        => _today = DateOnly.Parse(date);
+
+    [When("the domain asks the ACL to open a zaak")]
+    public async Task WhenTheDomainAsksTheAclToOpenAZaak()
+    {
+        var service = new AclService(_gateway, _defaults!, new FixedClock(_today));
+        _returnedUrl = await service.OpenZaakAsync(_registration!);
+    }
+
+    [Then("a zaak is created with these default-filled fields")]
+    public void ThenAZaakIsCreatedWithTheseDefaultFilledFields(DataTable expected)
+    {
+        var request = Assert.IsType<ZaakRequest>(_gateway.Captured);
+        var fields = ToFieldMap(expected);
+        Assert.Equal(fields["bronorganisatie"], request.Bronorganisatie);
+        Assert.Equal(fields["verantwoordelijkeOrganisatie"], request.VerantwoordelijkeOrganisatie);
+        Assert.Equal(fields["vertrouwelijkheidaanduiding"], request.Vertrouwelijkheidaanduiding);
+        Assert.Equal(fields["zaaktype"], request.Zaaktype.ToString());
+        Assert.Equal(fields["startdatum"], request.Startdatum.ToString("yyyy-MM-dd"));
+    }
+
+    [Then("the ACL returns the URL of the created zaak")]
+    public void ThenTheAclReturnsTheUrlOfTheCreatedZaak()
+        => Assert.Equal(InMemoryZaakGateway.CreatedZaakUrl, _returnedUrl);
+
+    private static Dictionary<string, string> ToFieldMap(DataTable table)
+        => table.Rows.ToDictionary(r => r["field"], r => r["value"]);
+}

tests/acceptance/Support/FixedClock.cs

@@ -0,0 +1,10 @@
+using Acl.Application;
+
+namespace Acceptance.Support;
+
+/// <summary>A clock pinned to a known date so <c>startdatum</c> is deterministic
+/// in scenarios (ADR-0003).</summary>
+public sealed class FixedClock(DateOnly today) : IClock
+{
+    public DateOnly Today { get; } = today;
+}

tests/acceptance/Support/InMemoryZaakGateway.cs

@@ -0,0 +1,20 @@
+using Acl.Application;
+
+namespace Acceptance.Support;
+
+/// <summary>An in-memory stand-in for the OpenZaak Zaken API. It captures the
+/// fully default-filled <see cref="ZaakRequest"/> the ACL builds and returns a
+/// fixed zaak URL, so the acceptance scenario can verify the use case without a
+/// running OpenZaak (real-OpenZaak verification is a separate slice).</summary>
+public sealed class InMemoryZaakGateway : IZaakGateway
+{
+    public static readonly Uri CreatedZaakUrl = new("http://openzaak/zaken/api/v1/zaken/created-123");
+
+    public ZaakRequest? Captured { get; private set; }
+
+    public Task<Uri> OpenZaakAsync(ZaakRequest request, CancellationToken ct = default)
+    {
+        Captured = request;
+        return Task.FromResult(CreatedZaakUrl);
+    }
+}