Fix MySQL existence check and add router/store tests

- MySQL UPDATE returns 0 affected rows when values are unchanged, so
  detect existence via SELECT within the transaction instead.
- Add integration tests for PUT /locations/:id in createRouter.test.ts.
- Add changeset for catalog-react catalogApiMock update.

Signed-off-by: Fredrik Adelöw <freben@spotify.com>
Made-with: Cursor

.changeset/location-entity-ref-catalog-react.md

@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-catalog-react': patch
+---
+
+Updated `catalogApiMock` to include the new `updateLocation` method stub, keeping it in sync with the `CatalogApi` interface.

plugins/catalog-backend/src/providers/DefaultLocationStore.ts

@@ -210,16 +210,19 @@ export class DefaultLocationStore implements LocationStore, EntityProvider {
       throw new Error('location store is not initialized');
     }
 
-    // MySQL doesn't support UPDATE ... RETURNING, so we fall back to checking
-    // the affected row count and then doing a separate SELECT.
+    // MySQL doesn't support UPDATE ... RETURNING. MySQL also reports 0 affected
+    // rows when the new values are identical to the old ones, so we can't rely
+    // on the row count to detect existence. Instead we SELECT to check existence
+    // first and then UPDATE inside a transaction.
     let row: DbLocationsRow | undefined;
     if (this.db.client.config.client.includes('mysql')) {
       await this.db.transaction(async tx => {
-        const count = await tx<DbLocationsRow>('locations')
-          .where({ id })
-          .update({ type: location.type, target: location.target });
-        if (Number(count) > 0) {
-          [row] = await tx<DbLocationsRow>('locations').where({ id }).select();
+        [row] = await tx<DbLocationsRow>('locations').where({ id }).select();
+        if (row) {
+          await tx<DbLocationsRow>('locations')
+            .where({ id })
+            .update({ type: location.type, target: location.target });
+          row = { ...row, type: location.type, target: location.target };
         }
       });
     } else {

plugins/catalog-backend/src/service/createRouter.test.ts

@@ -1175,6 +1175,43 @@ describe('createRouter readonly disabled', () => {
     });
   });
 
+  describe('PUT /locations/:id', () => {
+    it('rejects malformed body', async () => {
+      const response = await request(app)
+        .put('/locations/foo')
+        .send({ typez: 'url', target: 'https://example.com' });
+
+      expect(locationService.updateLocation).not.toHaveBeenCalled();
+      expect(response.status).toEqual(400);
+    });
+
+    it('updates the location and returns it', async () => {
+      const spec: LocationInput = {
+        type: 'url',
+        target: 'https://example.com/new',
+      };
+
+      locationService.updateLocation.mockResolvedValue({
+        id: 'foo',
+        ...spec,
+        entityRef: 'location:default/generated-foo',
+      });
+
+      const response = await request(app).put('/locations/foo').send(spec);
+
+      expect(locationService.updateLocation).toHaveBeenCalledTimes(1);
+      expect(locationService.updateLocation).toHaveBeenCalledWith('foo', spec, {
+        credentials: mockCredentials.user(),
+      });
+      expect(response.status).toEqual(200);
+      expect(response.body).toEqual({
+        id: 'foo',
+        ...spec,
+        entityRef: 'location:default/generated-foo',
+      });
+    });
+  });
+
   describe('GET /locations/by-entity/:kind/:namespace/:name', () => {
     it('happy path: gets location by entity ref', async () => {
       const location: Location = {