test(domain): a citizen can withdraw an open registration → INGETROKKEN (refs #12)

Withdraw is allowed from INGEDIEND or IN_BEHANDELING, needs no zaak, is idempotent, and is

rejected once the registration has been decided (INGESCHREVEN/AFGEWEZEN). The WithdrawRegistration

handler loads, withdraws, and persists; a repeated withdrawal is a no-op.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

services/domain/Big.Tests/RegistrationTests.cs

@@ -217,4 +217,72 @@ public class RegistrationTests
         Assert.Contains("Afgewezen", rejectEx.Message);
         Assert.Equal(RegistrationStatus.Afgewezen, registration.Status);
     }
+
+    [Fact]
+    public void Withdrawing_an_ingediend_registration_sets_it_ingetrokken()
+    {
+        var registration = Registration.Submit("123456782");
+
+        registration.Withdraw();
+
+        Assert.Equal(RegistrationStatus.Ingetrokken, registration.Status);
+    }
+
+    [Fact]
+    public void Withdrawing_an_in_behandeling_registration_sets_it_ingetrokken()
+    {
+        // A citizen can still pull a registration back while a behandelaar has it in behandeling.
+        var registration = Registration.Submit("123456782");
+        registration.TakeIntoBehandeling();
+
+        registration.Withdraw();
+
+        Assert.Equal(RegistrationStatus.Ingetrokken, registration.Status);
+    }
+
+    [Fact]
+    public void Withdrawing_needs_no_zaak()
+    {
+        // Withdrawal is the citizen's own action and does not depend on the zaak having been opened.
+        var registration = Registration.Submit("123456782");
+
+        registration.Withdraw();
+
+        Assert.Equal(RegistrationStatus.Ingetrokken, registration.Status);
+        Assert.Null(registration.ZaakUrl);
+    }
+
+    [Fact]
+    public void Re_withdrawing_an_already_ingetrokken_registration_is_idempotent()
+    {
+        var registration = Registration.Submit("123456782");
+        registration.Withdraw();
+
+        registration.Withdraw();
+
+        Assert.Equal(RegistrationStatus.Ingetrokken, registration.Status);
+    }
+
+    [Fact]
+    public void Withdrawing_an_approved_registration_is_rejected()
+    {
+        var registration = Registration.Submit("123456782");
+        registration.AttachZaak(new Uri("http://openzaak/zaken/api/v1/zaken/abc"));
+        registration.Approve();
+
+        var ex = Assert.Throws<InvalidOperationException>(() => registration.Withdraw());
+        Assert.Contains("only an INGEDIEND", ex.Message);
+        Assert.Equal(RegistrationStatus.Ingeschreven, registration.Status);
+    }
+
+    [Fact]
+    public void Withdrawing_a_rejected_registration_is_rejected()
+    {
+        var registration = Registration.Submit("123456782");
+        registration.Reject();
+
+        var ex = Assert.Throws<InvalidOperationException>(() => registration.Withdraw());
+        Assert.Contains("only an INGEDIEND", ex.Message);
+        Assert.Equal(RegistrationStatus.Afgewezen, registration.Status);
+    }
 }