diff --git a/.github/workflows/rails_application-coverage.yml b/.github/workflows/rails_application-coverage.yml
index 8f2ea509..a5222f01 100644
--- a/.github/workflows/rails_application-coverage.yml
+++ b/.github/workflows/rails_application-coverage.yml
@@ -14,6 +14,7 @@ on:
     paths:
       - "apps/rails_application/Gemfile.lock"
       - ".github/workflows/rails_application-coverage.yml"
+      - "apps/rails_application/test/test_helper.rb"
   schedule:
     - cron: '0 17 * * *'
 jobs:
@@ -59,8 +60,15 @@ jobs:
           ruby-version: ruby-3.4.6
           bundler-cache: true
           working-directory: apps/rails_application
+      - name: Prepare test database
+        run: bin/rails db:test:prepare
+        working-directory: apps/rails_application
+        env:
+          DATABASE_URL: "postgres://postgres:secret@localhost:5432/cqrs-es-sample-with-res_test"
+          RAILS_ENV: test
       - name: Run full mutation testing
-        run: make -C apps/rails_application mutate
+        run: RAILS_ENV=test bundle exec mutant run --jobs 1
+        working-directory: apps/rails_application
         env:
           DATABASE_URL: "postgres://postgres:secret@localhost:5432/cqrs-es-sample-with-res_test"
           RAILS_ENV: test
diff --git a/apps/rails_application/Makefile b/apps/rails_application/Makefile
index 3898e74f..f5212855 100644
--- a/apps/rails_application/Makefile
+++ b/apps/rails_application/Makefile
@@ -7,6 +7,8 @@ dev:
 	@$(MAKE) -j 2 web css
 
 mutate: ## Run full mutation tests
+	@echo "Preparing test database..."
+	@RAILS_ENV=test bin/rails db:test:prepare
 	@echo "Running full mutation tests..."
 	@RAILS_ENV=test bundle exec mutant run
 
diff --git a/apps/rails_application/test/invoices/assign_store_to_invoice_test.rb b/apps/rails_application/test/invoices/assign_store_to_invoice_test.rb
index 439deb91..4768a44b 100644
--- a/apps/rails_application/test/invoices/assign_store_to_invoice_test.rb
+++ b/apps/rails_application/test/invoices/assign_store_to_invoice_test.rb
@@ -91,5 +91,37 @@ def test_assigns_store_to_correct_invoice_when_multiple_invoices_exist
       assert_equal(store_id_1, invoice_1.store_id)
       assert_equal(store_id_2, invoice_2.store_id)
     end
+
+    def test_returns_nil_when_invoice_exists_in_different_store
+      event_store = Rails.configuration.event_store
+      store_id_1 = SecureRandom.uuid
+      store_id_2 = SecureRandom.uuid
+      invoice_id = SecureRandom.uuid
+
+      event_store.publish(
+        Invoicing::InvoiceItemAdded.new(
+          data: {
+            invoice_id: invoice_id,
+            product_id: SecureRandom.uuid,
+            title: "Test Product",
+            quantity: 1,
+            unit_price: 100,
+            vat_rate: { rate: 20, code: "VAT" }
+          }
+        )
+      )
+
+      event_store.publish(
+        Stores::InvoiceRegistered.new(
+          data: {
+            store_id: store_id_1,
+            invoice_id: invoice_id
+          }
+        )
+      )
+
+      assert_nil Invoices.find_invoice_in_store(invoice_id, store_id_2)
+      assert_not_nil Invoices.find_invoice_in_store(invoice_id, store_id_1)
+    end
   end
 end
diff --git a/apps/rails_application/test/test_helper.rb b/apps/rails_application/test/test_helper.rb
index 5f5bfb79..1bbc3e48 100644
--- a/apps/rails_application/test/test_helper.rb
+++ b/apps/rails_application/test/test_helper.rb
@@ -142,6 +142,7 @@ def before_setup
 
     Configuration.new.call(Rails.configuration.event_store, Rails.configuration.command_bus)
     @default_store_id = ensure_default_store
+    cookies[:current_store_id] = @default_store_id
     result
   end