diff --git a/tests/test_customers.py b/tests/test_customers.py
new file mode 100644
index 00000000..b9c4e659
--- /dev/null
+++ b/tests/test_customers.py
@@ -0,0 +1,22 @@
+import pytest
+
+from advancedbilling.exceptions.customer_error_response_exception import CustomerErrorResponseException
+from advancedbilling.controllers.customers_controller import CustomersController
+from advancedbilling.models.create_customer_request import CreateCustomerRequest
+from tests.data import InitCases
+
+
+class TestCustomers:
+    def test_invalid_customer_creation_throws_422_error(self, customers_controller: CustomersController):
+        customer_request = CreateCustomerRequest(InitCases.get_customer_request())
+        customers_controller.create_customer(
+            customer_request
+        )
+
+        with pytest.raises(CustomerErrorResponseException) as e:
+            customers_controller.create_customer(
+                customer_request
+            )
+
+        assert e.value.response_code == 422
+        assert e.value.errors == ['Reference: must be unique - that value has been taken.']
\ No newline at end of file
diff --git a/tests/test_invoices.py b/tests/test_invoices.py
index c7a220a5..22c44bd1 100644
--- a/tests/test_invoices.py
+++ b/tests/test_invoices.py
@@ -244,11 +244,11 @@ def test_create_invoice_given_invalid_period_range_end_value_then_should_throw_e
                 CreateInvoiceRequest(InitCases.get_invoice_request_with_invalid_period()),
             )
 
-            errors = exception_info.value.errors
+        errors = exception_info.value.errors
 
-            assert exception_info.value.response_code == 422
-            assert len(errors) == 1
-            assert errors == {"line_items[0].period_range_end": ["Must be greater or equal to period_range_start."]}
+        assert exception_info.value.response_code == 422
+        assert len(errors) == 1
+        assert errors == {"line_items[0].period_range_end": ["Must be greater or equal to period_range_start."]}
 
         subscriptions_controller.purge_subscription(subscription.id, customer.id)
         customers_controller.delete_customer(customer.id)
diff --git a/tests/test_subscriptions.py b/tests/test_subscriptions.py
index a097d0ef..c5be3b0b 100644
--- a/tests/test_subscriptions.py
+++ b/tests/test_subscriptions.py
@@ -141,8 +141,8 @@ def test_create_subscription_given_existing_product_and_not_existing_customer_th
                 )
             )
 
-            assert e.value.response_code == 422
-            assert e.value.message == "A Customer must be specified for the subscription to be valid."
+        assert e.value.response_code == 422
+        assert e.value.errors == ["A Customer must be specified for the subscription to be valid."]
 
     def test_create_subscription_given_invalid_credentials_then_thrown_exception_with_401_status_code(
         self,
@@ -159,7 +159,7 @@ def test_create_subscription_given_invalid_credentials_then_thrown_exception_wit
                 )
             )
 
-            assert e.value.response_code == 401
+        assert e.value.response_code == 401
 
     def test_list_subscriptions_filtering_by_metadata_given_filter_by_metadata_then_return_subscription_having_this_metadata(
         self,