Adjusted sample to showcase idempotence handling

src/guestStayAccounts/api/api.e2e.spec.ts

@@ -147,10 +147,10 @@ void describe('guestStayAccount E2E', () => {
   void describe('When checked in', () => {
     const checkedInAccount: TestRequest = checkIn;
 
-    void it(`doesn't check in`, () =>
+    void it(`ignores check in`, () =>
       given(checkedInAccount)
         .when(checkIn)
-        .then([expectError(403, { detail: `Guest is already checked-in!` })]));
+        .then([expectResponse(201)]));
 
     void it('records charge', () =>
       given(checkedInAccount)
@@ -299,10 +299,10 @@ void describe('guestStayAccount E2E', () => {
           expectError(403, { detail: `Guest account is already checked out` }),
         ]));
 
-    void it(`doesn't checkout`, () =>
+    void it(`ignores checkout`, () =>
       given(...checkedOutAccount)
         .when(checkOut)
-        .then([expectError(403, { detail: `NotCheckedIn` })]));
+        .then([expectResponse(204)]));
 
     void it(`details return 404`, () =>
       given(...checkedOutAccount)

src/guestStayAccounts/api/api.int.spec.ts

@@ -126,10 +126,8 @@ void describe('Guest stay account', () => {
         ])),
     );
 
-    void it(`doesn't check in`, () =>
-      given(checkedInAccount)
-        .when(checkIn)
-        .then(expectError(403, { detail: `Guest is already checked-in!` })));
+    void it(`ingores check in`, () =>
+      given(checkedInAccount).when(checkIn).then(expectResponse(201)));
 
     void it('records charge', () =>
       given(checkedInAccount)
@@ -422,23 +420,10 @@ void describe('Guest stay account', () => {
           expectError(403, { detail: `Guest account is already checked out` }),
         ));
 
-    void it(`doesn't checkout`, () =>
+    void it(`ignores check out`, () =>
       given(checkedOutAccount)
         .when(checkOut)
-        .then([
-          expectError(403, { detail: `NotCheckedIn` }),
-          expectNewEvents(guestStayAccountId, [
-            {
-              type: 'GuestCheckoutFailed',
-              data: {
-                guestStayAccountId,
-                groupCheckoutId: undefined,
-                reason: 'NotCheckedIn',
-                failedAt: now,
-              },
-            },
-          ]),
-        ]));
+        .then([expectResponse(204)]));
   });
 
   const given = ApiSpecification.for<GuestStayAccountEvent>(

src/guestStayAccounts/api/api.ts

@@ -168,16 +168,17 @@ export const guestStayAccountsApi =
           metadata: { now: getCurrentTime() },
         };
 
-        const {
-          newEvents: [event],
-        } = await handle(eventStore, guestStayAccountId, (state) =>
-          checkOut(command, state),
+        const { newEvents } = await handle(
+          eventStore,
+          guestStayAccountId,
+          (state) => checkOut(command, state),
         );
 
-        return event.type !== 'GuestCheckoutFailed'
+        return newEvents.length === 0 ||
+          newEvents[0].type !== 'GuestCheckoutFailed'
           ? NoContent()
           : Forbidden({
-              problemDetails: event.data.reason,
+              problemDetails: newEvents[0].data.reason,
             });
       }),
     );

src/guestStayAccounts/businessLogic.ts

@@ -54,8 +54,11 @@ export type GuestStayCommand =
 export const checkIn = (
   { data: { guestId, roomId }, metadata }: CheckIn,
   state: GuestStayAccount,
-): GuestCheckedIn => {
-  assertDoesNotExist(state);
+): GuestCheckedIn | [] => {
+  if (state.status === 'CheckedIn') [];
+
+  if (state.status === 'CheckedOut')
+    throw new IllegalStateError(`Guest account is already checked out`);
 
   const now = metadata?.now ?? new Date();
 
@@ -107,7 +110,9 @@ export const recordPayment = (
 export const checkOut = (
   { data: { guestStayAccountId, groupCheckoutId }, metadata }: CheckOut,
   state: GuestStayAccount,
-): GuestCheckedOut | GuestCheckoutFailed => {
+): GuestCheckedOut | GuestCheckoutFailed | [] => {
+  if (state.status === 'CheckedOut') return [];
+
   const now = metadata?.now ?? new Date();
 
   if (state.status !== 'CheckedIn')
@@ -146,7 +151,7 @@ export const checkOut = (
 export const decide = (
   command: GuestStayCommand,
   state: GuestStayAccount,
-): GuestStayAccountEvent => {
+): GuestStayAccountEvent | GuestStayAccountEvent[] => {
   const { type } = command;
 
   switch (type) {
@@ -165,16 +170,6 @@ export const decide = (
   }
 };
 
-const assertDoesNotExist = (state: GuestStayAccount): state is CheckedIn => {
-  if (state.status === 'CheckedIn')
-    throw new IllegalStateError(`Guest is already checked-in!`);
-
-  if (state.status === 'CheckedOut')
-    throw new IllegalStateError(`Guest account is already checked out`);
-
-  return true;
-};
-
 const assertIsCheckedIn = (state: GuestStayAccount): state is CheckedIn => {
   if (state.status === 'NotExisting')
     throw new IllegalStateError(`Guest account doesn't exist!`);

src/guestStayAccounts/businessLogic.unit.spec.ts

@@ -121,7 +121,7 @@ void describe('Guest Stay Account', () => {
       },
     ];
 
-    void it(`doesn't check in`, () =>
+    void it(`ignores check in`, () =>
       given(checkedInAccount)
         .when({
           type: 'CheckIn',
@@ -131,9 +131,7 @@ void describe('Guest Stay Account', () => {
           },
           metadata: { now },
         })
-        .thenThrows<IllegalStateError>(
-          (error) => error.message === `Guest is already checked-in!`,
-        ));
+        .then([]));
 
     void it('records charge', () => {
       given(checkedInAccount)
@@ -476,7 +474,7 @@ void describe('Guest Stay Account', () => {
           (error) => error.message === `Guest account is already checked out`,
         ));
 
-    void it(`doesn't checkout`, () =>
+    void it(`ignores check out`, () =>
       given(checkedOutAccount)
         .when({
           type: 'CheckOut',
@@ -485,16 +483,6 @@ void describe('Guest Stay Account', () => {
           },
           metadata: { now },
         })
-        .then([
-          {
-            type: 'GuestCheckoutFailed',
-            data: {
-              guestStayAccountId,
-              groupCheckoutId: undefined,
-              reason: 'NotCheckedIn',
-              failedAt: now,
-            },
-          },
-        ]));
+        .then([]));
   });
 });