Align rent payment dialog validation (#55)

backend/src/main/java/fr/nessar/lmnporganizer/rental/adapter/in/web/rent/RentPaymentApi.java

@@ -16,6 +16,12 @@ import java.util.List;
 final class RentPaymentApi {
 private RentPaymentApi() {}
 
+record ConcurrentChangeResponse(String code, String message) {}
+
+record FieldErrorResponse(String field, String code) {}
+
+record ValidationFailureResponse(String code, List<FieldErrorResponse> errors) {}
+
 record CreateRequest(
 	@NotBlank String operationId,
 	@NotBlank String rentDueId,

backend/src/main/java/fr/nessar/lmnporganizer/rental/adapter/in/web/rent/RentPaymentController.java

@@ -6,7 +6,9 @@ import fr.nessar.lmnporganizer.rental.application.rent.GeneratePaymentReceiptSer
 import fr.nessar.lmnporganizer.rental.application.rent.RecordRentPaymentService;
 import fr.nessar.lmnporganizer.rental.application.rent.RefundRentPaymentService;
 import fr.nessar.lmnporganizer.rental.application.rent.RentPaymentHistoryService;
+import fr.nessar.lmnporganizer.rental.application.rent.RentPaymentValidationFailure;
 import fr.nessar.lmnporganizer.rental.application.rent.ReverseRentPaymentService;
+import fr.nessar.lmnporganizer.rental.application.shared.ConcurrentChange;
 import fr.nessar.lmnporganizer.rental.application.shared.GeneratedDocument;
 import fr.nessar.lmnporganizer.rental.domain.landlord.LandlordId;
 import fr.nessar.lmnporganizer.rental.domain.lease.LeaseId;
@@ -16,12 +18,14 @@ import jakarta.validation.Valid;
 import java.time.DateTimeException;
 import java.time.ZoneId;
 import java.util.List;
+import org.springframework.dao.OptimisticLockingFailureException;
 import org.springframework.http.ContentDisposition;
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpStatus;
 import org.springframework.http.ResponseEntity;
 import org.springframework.security.core.annotation.AuthenticationPrincipal;
 import org.springframework.security.oauth2.core.oidc.user.OidcUser;
+import org.springframework.web.bind.annotation.ExceptionHandler;
 import org.springframework.web.bind.annotation.GetMapping;
 import org.springframework.web.bind.annotation.PathVariable;
 import org.springframework.web.bind.annotation.PostMapping;
@@ -58,6 +62,26 @@ public RentPaymentController(
 	this.authenticatedLandlord = authenticatedLandlord;
 }
 
+@ExceptionHandler({ConcurrentChange.class, OptimisticLockingFailureException.class})
+ResponseEntity<RentPaymentApi.ConcurrentChangeResponse> concurrentChange(
+	RuntimeException exception) {
+	return ResponseEntity.status(HttpStatus.CONFLICT)
+		.body(
+			new RentPaymentApi.ConcurrentChangeResponse(
+				ConcurrentChange.CODE,
+				"La ressource a été modifiée ; rechargez-la puis réessayez."));
+}
+
+@ExceptionHandler(RentPaymentValidationFailure.class)
+ResponseEntity<RentPaymentApi.ValidationFailureResponse> invalidPayment(
+	RentPaymentValidationFailure failure) {
+	return ResponseEntity.badRequest()
+		.body(
+			new RentPaymentApi.ValidationFailureResponse(
+				"validation_failed",
+				List.of(new RentPaymentApi.FieldErrorResponse(failure.field(), failure.code()))));
+}
+
 @GetMapping
 List<RentPaymentApi.Response> list(
 	@AuthenticationPrincipal OidcUser principal, @RequestParam(required = false) String leaseId) {

backend/src/main/java/fr/nessar/lmnporganizer/rental/application/rent/AllocateRentPaymentService.java

@@ -13,7 +13,7 @@ import fr.nessar.lmnporganizer.rental.domain.rent.RentDueSettlement;
 import fr.nessar.lmnporganizer.rental.domain.rent.RentPayment;
 import fr.nessar.lmnporganizer.rental.domain.rent.RentPaymentId;
 import fr.nessar.lmnporganizer.rental.domain.rent.RentPaymentRepository;
-import fr.nessar.lmnporganizer.rental.domain.rent.RentRuleViolation;
+import fr.nessar.lmnporganizer.rental.domain.rent.RentPaymentStatus;
 import java.math.BigDecimal;
 import java.time.Clock;
 import java.time.LocalDate;
@@ -67,6 +67,9 @@ public RentPayment allocate(
 		if (payment.version() != paymentVersion) {
 			throw new ConcurrentChange("Rent payment");
 		}
+		if (payment.status() != RentPaymentStatus.CONFIRMED) {
+			throw new RentPaymentConflict("Un règlement contrepassé ne peut pas être affecté.");
+		}
 		RentDue due =
 			rentDues
 				.find(landlordId, rentDueId)
@@ -74,12 +77,34 @@ public RentPayment allocate(
 		if (due.version() != rentDueVersion) {
 			throw new ConcurrentChange("Rent due");
 		}
+		if (!payment.leaseId().equals(due.leaseId())) {
+			throw new RentPaymentValidationFailure(
+				"rentDueId",
+				"different_lease",
+				"Une affectation doit viser une échéance du même bail.");
+		}
+		if (payment.allocations().stream()
+			.anyMatch(allocation -> allocation.rentDueId().equals(due.id()))) {
+			throw new RentPaymentValidationFailure(
+				"rentDueId",
+				"already_allocated",
+				"Cette échéance a déjà reçu une affectation de ce règlement.");
+		}
 		if (due.settlement() == RentDueSettlement.PAID) {
 			throw new RentPaymentConflict(
 				"Une échéance déjà réglée ne peut pas recevoir une affectation.");
 		}
-		if (!payment.leaseId().equals(due.leaseId())) {
-			throw new RentRuleViolation("Une affectation doit viser une échéance du même bail.");
+		if (amount != null && amount.compareTo(payment.unallocatedBalance()) > 0) {
+			throw new RentPaymentValidationFailure(
+				"amount",
+				"exceeds_payment_balance",
+				"L'affectation dépasse le solde non affecté du règlement.");
+		}
+		if (amount != null && amount.compareTo(due.remainingAmount()) > 0) {
+			throw new RentPaymentValidationFailure(
+				"amount",
+				"exceeds_rent_due_balance",
+				"L'affectation dépasse le solde restant de l'échéance.");
 		}
 		PaymentAllocation allocation =
 			new PaymentAllocation(allocationId, due.id(), amount, LocalDate.now(clock));

backend/src/main/java/fr/nessar/lmnporganizer/rental/application/rent/RecordRentPaymentService.java

@@ -13,7 +13,6 @@ import fr.nessar.lmnporganizer.rental.domain.rent.RentDueSettlement;
 import fr.nessar.lmnporganizer.rental.domain.rent.RentPayment;
 import fr.nessar.lmnporganizer.rental.domain.rent.RentPaymentId;
 import fr.nessar.lmnporganizer.rental.domain.rent.RentPaymentRepository;
-import fr.nessar.lmnporganizer.rental.domain.rent.RentRuleViolation;
 import java.math.BigDecimal;
 import java.time.Clock;
 import java.time.LocalDate;
@@ -88,7 +87,10 @@ private RentPayment recordInTransaction(
 	BigDecimal amount) {
 	LocalDate today = LocalDate.now(clock.withZone(timeZone));
 	if (receivedAt == null || receivedAt.isAfter(today)) {
-	throw new RentRuleViolation("La date de réception du règlement ne peut pas être future.");
+	throw new RentPaymentValidationFailure(
+		"receivedAt",
+		"future_date",
+		"La date de réception du règlement ne peut pas être future.");
 	}
 	RentDue due =
 		rentDues.find(landlordId, rentDueId).orElseThrow(() -> new ResourceNotFound("Rent due"));

backend/src/main/java/fr/nessar/lmnporganizer/rental/application/rent/RefundRentPaymentService.java

@@ -10,7 +10,7 @@ import fr.nessar.lmnporganizer.rental.domain.rent.RentPaymentRefund;
 import fr.nessar.lmnporganizer.rental.domain.rent.RentPaymentRefundId;
 import fr.nessar.lmnporganizer.rental.domain.rent.RentPaymentRefundRepository;
 import fr.nessar.lmnporganizer.rental.domain.rent.RentPaymentRepository;
-import fr.nessar.lmnporganizer.rental.domain.rent.RentRuleViolation;
+import fr.nessar.lmnporganizer.rental.domain.rent.RentPaymentStatus;
 import java.math.BigDecimal;
 import java.time.Clock;
 import java.time.LocalDate;
@@ -71,12 +71,22 @@ private RentPayment refundInTransaction(
 	ZoneId timeZone) {
 	LocalDate today = LocalDate.now(clock.withZone(timeZone));
 	if (refundedAt == null || refundedAt.isAfter(today)) {
-	throw new RentRuleViolation("La date du remboursement ne peut pas être future.");
+	throw new RentPaymentValidationFailure(
+		"refundedAt", "future_date", "La date du remboursement ne peut pas être future.");
 	}
 	RentPayment payment = payment(landlordId, paymentId);
 	if (payment.version() != paymentVersion) {
 	throw new ConcurrentChange("Rent payment");
 	}
+	if (payment.status() != RentPaymentStatus.CONFIRMED) {
+	throw new RentPaymentConflict("Un règlement contrepassé ne peut pas être remboursé.");
+	}
+	if (amount != null && amount.compareTo(payment.unallocatedBalance()) > 0) {
+	throw new RentPaymentValidationFailure(
+		"amount",
+		"exceeds_unallocated_balance",
+		"Le remboursement dépasse le solde non affecté du règlement.");
+	}
 	RentPaymentRefund refund = RentPaymentRefund.recorded(refundId, payment, amount, refundedAt);
 	RentPayment saved = payments.save(payment);
 	refunds.save(refund);

backend/src/main/java/fr/nessar/lmnporganizer/rental/application/rent/RentPaymentValidationFailure.java

@@ -0,0 +1,22 @@
+package fr.nessar.lmnporganizer.rental.application.rent;
+
+import java.util.Objects;
+
+public final class RentPaymentValidationFailure extends RuntimeException {
+private final String field;
+private final String code;
+
+public RentPaymentValidationFailure(String field, String code, String message) {
+	super(message);
+	this.field = Objects.requireNonNull(field);
+	this.code = Objects.requireNonNull(code);
+}
+
+public String field() {
+	return field;
+}
+
+public String code() {
+	return code;
+}
+}

backend/src/main/java/fr/nessar/lmnporganizer/rental/application/shared/ConcurrentChange.java

@@ -1,6 +1,8 @@
 package fr.nessar.lmnporganizer.rental.application.shared;
 
 public final class ConcurrentChange extends RuntimeException {
+public static final String CODE = "concurrent_change";
+
 public ConcurrentChange(String resource) {
 	super(resource + " changed concurrently; reload it and retry.");
 }

backend/src/test/java/fr/nessar/lmnporganizer/rental/adapter/in/web/common/RentPaymentConflictContractTest.java

@@ -0,0 +1,19 @@
+package fr.nessar.lmnporganizer.rental.adapter.in.web.common;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import fr.nessar.lmnporganizer.rental.application.rent.RentPaymentConflict;
+import org.junit.jupiter.api.Test;
+import org.springframework.http.HttpStatus;
+
+class RentPaymentConflictContractTest {
+@Test
+void keepsBusinessConflictsAsUncoded409Responses() {
+	var response =
+		new RentalApiExceptionHandler().conflict(new RentPaymentConflict("Échéance déjà réglée"));
+
+	assertEquals(HttpStatus.CONFLICT, response.getStatusCode());
+	assertEquals(
+		new RentalApiExceptionHandler.ApiError("Échéance déjà réglée"), response.getBody());
+}
+}

backend/src/test/java/fr/nessar/lmnporganizer/rental/adapter/in/web/rent/RentPaymentControllerErrorTest.java

@@ -0,0 +1,64 @@
+package fr.nessar.lmnporganizer.rental.adapter.in.web.rent;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.mockito.Mockito.mock;
+
+import fr.nessar.lmnporganizer.rental.adapter.in.web.common.AuthenticatedLandlord;
+import fr.nessar.lmnporganizer.rental.application.rent.AllocateRentPaymentService;
+import fr.nessar.lmnporganizer.rental.application.rent.GeneratePaymentReceiptService;
+import fr.nessar.lmnporganizer.rental.application.rent.RecordRentPaymentService;
+import fr.nessar.lmnporganizer.rental.application.rent.RefundRentPaymentService;
+import fr.nessar.lmnporganizer.rental.application.rent.RentPaymentHistoryService;
+import fr.nessar.lmnporganizer.rental.application.rent.RentPaymentValidationFailure;
+import fr.nessar.lmnporganizer.rental.application.rent.ReverseRentPaymentService;
+import fr.nessar.lmnporganizer.rental.application.shared.ConcurrentChange;
+import java.util.List;
+import org.junit.jupiter.api.Test;
+import org.springframework.http.HttpStatus;
+
+class RentPaymentControllerErrorTest {
+@Test
+void mapsPaymentInputFailuresToTheStableValidationContract() {
+	RentPaymentController controller =
+		new RentPaymentController(
+			mock(RentPaymentHistoryService.class),
+			mock(RecordRentPaymentService.class),
+			mock(AllocateRentPaymentService.class),
+			mock(RefundRentPaymentService.class),
+			mock(ReverseRentPaymentService.class),
+			mock(GeneratePaymentReceiptService.class),
+			mock(AuthenticatedLandlord.class));
+
+	var response =
+		controller.invalidPayment(
+			new RentPaymentValidationFailure(
+				"amount", "exceeds_unallocated_balance", "Le remboursement dépasse le solde."));
+
+	assertEquals(HttpStatus.BAD_REQUEST, response.getStatusCode());
+	assertEquals(
+		new RentPaymentApi.ValidationFailureResponse(
+			"validation_failed",
+			List.of(
+				new RentPaymentApi.FieldErrorResponse("amount", "exceeds_unallocated_balance"))),
+		response.getBody());
+}
+
+@Test
+void mapsOnlyConcurrentChangesToTheCodedStaleContract() {
+	var response = controller().concurrentChange(new ConcurrentChange("Rent payment"));
+
+	assertEquals(HttpStatus.CONFLICT, response.getStatusCode());
+	assertEquals(ConcurrentChange.CODE, response.getBody().code());
+}
+
+private static RentPaymentController controller() {
+	return new RentPaymentController(
+		mock(RentPaymentHistoryService.class),
+		mock(RecordRentPaymentService.class),
+		mock(AllocateRentPaymentService.class),
+		mock(RefundRentPaymentService.class),
+		mock(ReverseRentPaymentService.class),
+		mock(GeneratePaymentReceiptService.class),
+		mock(AuthenticatedLandlord.class));
+}
+}

backend/src/test/java/fr/nessar/lmnporganizer/rental/application/rent/AllocateRentPaymentServiceTest.java

@@ -198,6 +198,116 @@ void staleVersionsAndAlreadyPaidDueCreateNoAllocation() {
 	verify(payments, never()).save(any());
 }
 
+@Test
+void reversedPaymentCannotReceiveAnotherAllocation() {
+	RentPaymentRepository payments = mock(RentPaymentRepository.class);
+	RentDueRepository rentDues = mock(RentDueRepository.class);
+	RentPayment payment =
+		RentPayment.reconstitute(
+			PAYMENT_ID,
+			LANDLORD_ID,
+			LEASE_ID,
+			LocalDate.of(2026, 2, 2),
+			new BigDecimal("100"),
+			RentPaymentStatus.REVERSED,
+			List.of(),
+			BigDecimal.ZERO,
+			LocalDate.of(2026, 2, 2),
+			4);
+	when(payments.find(LANDLORD_ID, PAYMENT_ID)).thenReturn(Optional.of(payment));
+
+	assertThrows(
+		RentPaymentConflict.class,
+		() ->
+			new AllocateRentPaymentService(payments, rentDues, new RecordingTransactions(), CLOCK)
+				.allocate(
+					LANDLORD_ID, PAYMENT_ID, "operation-2", 4, DUE_ID, 2, new BigDecimal("10")));
+
+	verifyNoInteractions(rentDues);
+	verify(payments, never()).save(any());
+}
+
+@Test
+void allocationMapsDuplicateAndBalanceFailuresToFields() {
+	RentPaymentRepository payments = mock(RentPaymentRepository.class);
+	RentDueRepository rentDues = mock(RentDueRepository.class);
+	PaymentAllocation existing =
+		new PaymentAllocation(
+			new PaymentAllocationId("allocation-1"),
+			DUE_ID,
+			new BigDecimal("10"),
+			LocalDate.of(2026, 2, 2));
+	RentPayment payment =
+		RentPayment.reconstitute(
+			PAYMENT_ID,
+			LANDLORD_ID,
+			LEASE_ID,
+			LocalDate.of(2026, 2, 2),
+			new BigDecimal("100"),
+			RentPaymentStatus.CONFIRMED,
+			List.of(existing),
+			BigDecimal.ZERO,
+			LocalDate.of(2026, 2, 2),
+			4);
+	RentDue due =
+		RentDue.reconstitute(
+			DUE_ID,
+			LANDLORD_ID,
+			LEASE_ID,
+			YearMonth.of(2026, 2),
+			LocalDate.of(2026, 3, 5),
+			new BigDecimal("50"),
+			BigDecimal.ZERO,
+			new BigDecimal("10"),
+			2);
+	when(payments.find(LANDLORD_ID, PAYMENT_ID)).thenReturn(Optional.of(payment));
+	when(rentDues.find(LANDLORD_ID, DUE_ID)).thenReturn(Optional.of(due));
+	AllocateRentPaymentService service =
+		new AllocateRentPaymentService(payments, rentDues, new RecordingTransactions(), CLOCK);
+
+	RentPaymentValidationFailure duplicate =
+		assertThrows(
+			RentPaymentValidationFailure.class,
+			() ->
+				service.allocate(
+					LANDLORD_ID, PAYMENT_ID, "operation-2", 4, DUE_ID, 2, new BigDecimal("10")));
+	assertEquals("rentDueId", duplicate.field());
+	assertEquals("already_allocated", duplicate.code());
+
+	RentPayment otherPayment =
+		RentPayment.reconstitute(
+			PAYMENT_ID,
+			LANDLORD_ID,
+			LEASE_ID,
+			LocalDate.of(2026, 2, 2),
+			new BigDecimal("100"),
+			RentPaymentStatus.CONFIRMED,
+			List.of(),
+			BigDecimal.ZERO,
+			LocalDate.of(2026, 2, 2),
+			4);
+	when(payments.find(LANDLORD_ID, PAYMENT_ID)).thenReturn(Optional.of(otherPayment));
+	RentPaymentValidationFailure balance =
+		assertThrows(
+			RentPaymentValidationFailure.class,
+			() ->
+				service.allocate(
+					LANDLORD_ID, PAYMENT_ID, "operation-3", 4, DUE_ID, 2, new BigDecimal("101")));
+	assertEquals("amount", balance.field());
+	assertEquals("exceeds_payment_balance", balance.code());
+	RentPaymentValidationFailure dueBalance =
+		assertThrows(
+			RentPaymentValidationFailure.class,
+			() ->
+				service.allocate(
+					LANDLORD_ID, PAYMENT_ID, "operation-4", 4, DUE_ID, 2, new BigDecimal("41")));
+	assertEquals("amount", dueBalance.field());
+	assertEquals("exceeds_rent_due_balance", dueBalance.code());
+
+	verify(rentDues, never()).save(any());
+	verify(payments, never()).save(any());
+}
+
 private static final class RecordingTransactions implements TransactionRunner {
 	private int calls;
 

backend/src/test/java/fr/nessar/lmnporganizer/rental/application/rent/RecordRentPaymentServiceTest.java

@@ -23,7 +23,6 @@ import fr.nessar.lmnporganizer.rental.domain.rent.RentPayment;
 import fr.nessar.lmnporganizer.rental.domain.rent.RentPaymentId;
 import fr.nessar.lmnporganizer.rental.domain.rent.RentPaymentRepository;
 import fr.nessar.lmnporganizer.rental.domain.rent.RentPaymentStatus;
-import fr.nessar.lmnporganizer.rental.domain.rent.RentRuleViolation;
 import java.math.BigDecimal;
 import java.time.Clock;
 import java.time.Instant;
@@ -208,17 +207,20 @@ void staleOrPaidDueAndCashFromTheNextParisDayCreateNoPayment() {
 				LocalDate.of(2026, 2, 9),
 				PARIS,
 				new BigDecimal("1000")));
-	assertThrows(
-		RentRuleViolation.class,
-		() ->
-			service.record(
-				LANDLORD_ID,
-				"operation-1",
-				DUE_ID,
-				4,
-				LocalDate.of(2026, 2, 11),
-				PARIS,
-				new BigDecimal("1000")));
+	RentPaymentValidationFailure futureDate =
+		assertThrows(
+			RentPaymentValidationFailure.class,
+			() ->
+				service.record(
+					LANDLORD_ID,
+					"operation-1",
+					DUE_ID,
+					4,
+					LocalDate.of(2026, 2, 11),
+					PARIS,
+					new BigDecimal("1000")));
+	assertEquals("receivedAt", futureDate.field());
+	assertEquals("future_date", futureDate.code());
 	due.allocate(due.total());
 	assertThrows(
 		RentPaymentConflict.class,
@@ -262,7 +264,7 @@ void validatesReceivedDateInTheUsersCalendarZone() {
 
 	assertEquals(LocalDate.of(2026, 7, 19), LocalDate.now(boundary.withZone(PARIS)));
 	assertThrows(
-		RentRuleViolation.class,
+		RentPaymentValidationFailure.class,
 		() ->
 			service.record(
 				LANDLORD_ID,

backend/src/test/java/fr/nessar/lmnporganizer/rental/application/rent/RefundRentPaymentServiceTest.java

@@ -19,7 +19,6 @@ import fr.nessar.lmnporganizer.rental.domain.rent.RentPaymentRefundId;
 import fr.nessar.lmnporganizer.rental.domain.rent.RentPaymentRefundRepository;
 import fr.nessar.lmnporganizer.rental.domain.rent.RentPaymentRepository;
 import fr.nessar.lmnporganizer.rental.domain.rent.RentPaymentStatus;
-import fr.nessar.lmnporganizer.rental.domain.rent.RentRuleViolation;
 import java.math.BigDecimal;
 import java.time.Clock;
 import java.time.Instant;
@@ -168,17 +167,20 @@ void futureDateAndStalePaymentVersionCreateNoRefund() {
 	RefundRentPaymentService service =
 		new RefundRentPaymentService(payments, refunds, new RecordingTransactions(), CLOCK);
 
-	assertThrows(
-		RentRuleViolation.class,
-		() ->
-			service.refund(
-				LANDLORD_ID,
-				PAYMENT_ID,
-				"operation-1",
-				4,
-				new BigDecimal("50"),
-				LocalDate.of(2026, 2, 11),
-				PARIS));
+	RentPaymentValidationFailure futureDate =
+		assertThrows(
+			RentPaymentValidationFailure.class,
+			() ->
+				service.refund(
+					LANDLORD_ID,
+					PAYMENT_ID,
+					"operation-1",
+					4,
+					new BigDecimal("50"),
+					LocalDate.of(2026, 2, 11),
+					PARIS));
+	assertEquals("refundedAt", futureDate.field());
+	assertEquals("future_date", futureDate.code());
 	assertThrows(
 		ConcurrentChange.class,
 		() ->
@@ -190,6 +192,57 @@ void futureDateAndStalePaymentVersionCreateNoRefund() {
 				new BigDecimal("50"),
 				LocalDate.of(2026, 2, 9),
 				PARIS));
+	RentPaymentValidationFailure excessAmount =
+		assertThrows(
+			RentPaymentValidationFailure.class,
+			() ->
+				service.refund(
+					LANDLORD_ID,
+					PAYMENT_ID,
+					"operation-1",
+					4,
+					new BigDecimal("1001"),
+					LocalDate.of(2026, 2, 9),
+					PARIS));
+	assertEquals("amount", excessAmount.field());
+	assertEquals("exceeds_unallocated_balance", excessAmount.code());
+
+	verify(payments, never()).save(any());
+	verify(refunds, never()).save(any());
+}
+
+@Test
+void reversedPaymentCannotBeRefunded() {
+	RentPaymentRepository payments = mock(RentPaymentRepository.class);
+	RentPaymentRefundRepository refunds = mock(RentPaymentRefundRepository.class);
+	RentPayment payment =
+		RentPayment.reconstitute(
+			PAYMENT_ID,
+			LANDLORD_ID,
+			new LeaseId("lease-1"),
+			LocalDate.of(2026, 2, 2),
+			new BigDecimal("1000"),
+			RentPaymentStatus.REVERSED,
+			List.of(),
+			BigDecimal.ZERO,
+			LocalDate.of(2026, 2, 2),
+			4);
+	RentPaymentRefundId refundId = new RentPaymentRefundId("operation-1");
+	when(refunds.find(LANDLORD_ID, refundId)).thenReturn(Optional.empty());
+	when(payments.find(LANDLORD_ID, PAYMENT_ID)).thenReturn(Optional.of(payment));
+
+	assertThrows(
+		RentPaymentConflict.class,
+		() ->
+			new RefundRentPaymentService(payments, refunds, new RecordingTransactions(), CLOCK)
+				.refund(
+					LANDLORD_ID,
+					PAYMENT_ID,
+					"operation-1",
+					4,
+					new BigDecimal("50"),
+					LocalDate.of(2026, 2, 9),
+					PARIS));
 
 	verify(payments, never()).save(any());
 	verify(refunds, never()).save(any());
@@ -223,7 +276,7 @@ void validatesRefundDateInTheUsersCalendarZone() {
 
 	assertEquals(LocalDate.of(2026, 7, 19), LocalDate.now(boundary.withZone(PARIS)));
 	assertThrows(
-		RentRuleViolation.class,
+		RentPaymentValidationFailure.class,
 		() ->
 			service.refund(
 				LANDLORD_ID,

backend/src/test/java/fr/nessar/lmnporganizer/rental/domain/rent/RentPaymentTest.java

@@ -60,6 +60,7 @@ void refundsUseOnlySurplusAndReversalIsAuditableAndIdempotent() {
 @Test
 void confirmedPaymentMustRepresentPositiveCash() {
 	assertThrows(RentRuleViolation.class, () -> payment("0"));
+	assertEquals(new BigDecimal("0.001"), payment("0.001").amount());
 }
 
 private RentPayment payment(String amount) {