diff --git a/package.json b/package.json
index c0b4c4ef907..3acf628fd9c 100644
--- a/package.json
+++ b/package.json
@@ -25,7 +25,7 @@
   "devDependencies": {
     "@autorest/autorest": "^3.0.0",
     "@azure-tools/extension": "^3.0.249",
-    "@microsoft.azure/autorest.testserver": "^2.10.40"
+    "@microsoft.azure/autorest.testserver": "2.10.42"
   },
   "files": [
     "autorest/**/*.py",
diff --git a/test/vanilla/Expected/AcceptanceTests/BodyString/bodystring/aio/operations_async/_string_operations_async.py b/test/vanilla/Expected/AcceptanceTests/BodyString/bodystring/aio/operations_async/_string_operations_async.py
index 4ac4736575b..c71130a62f3 100644
--- a/test/vanilla/Expected/AcceptanceTests/BodyString/bodystring/aio/operations_async/_string_operations_async.py
+++ b/test/vanilla/Expected/AcceptanceTests/BodyString/bodystring/aio/operations_async/_string_operations_async.py
@@ -452,15 +452,15 @@ async def get_not_provided(
     async def get_base64_encoded(
         self,
         **kwargs
-    ) -> bytes:
+    ) -> bytearray:
         """Get value that is base64 encoded.
 
         :keyword callable cls: A custom type or function that will be passed the direct response
-        :return: bytes, or the result of cls(response)
-        :rtype: bytes
+        :return: bytearray, or the result of cls(response)
+        :rtype: bytearray
         :raises: ~azure.core.exceptions.HttpResponseError
         """
-        cls = kwargs.pop('cls', None)  # type: ClsType[bytes]
+        cls = kwargs.pop('cls', None)  # type: ClsType[bytearray]
         error_map = {404: ResourceNotFoundError, 409: ResourceExistsError}
         error_map.update(kwargs.pop('error_map', {}))
 
@@ -483,7 +483,7 @@ async def get_base64_encoded(
             error = self._deserialize(models.Error, response)
             raise HttpResponseError(response=response, model=error)
 
-        deserialized = self._deserialize('base64', pipeline_response)
+        deserialized = self._deserialize('bytearray', pipeline_response)
 
         if cls:
             return cls(pipeline_response, deserialized, {})
diff --git a/test/vanilla/Expected/AcceptanceTests/BodyString/bodystring/operations/_string_operations.py b/test/vanilla/Expected/AcceptanceTests/BodyString/bodystring/operations/_string_operations.py
index 486edc4ad09..c377ba629b9 100644
--- a/test/vanilla/Expected/AcceptanceTests/BodyString/bodystring/operations/_string_operations.py
+++ b/test/vanilla/Expected/AcceptanceTests/BodyString/bodystring/operations/_string_operations.py
@@ -466,15 +466,15 @@ def get_base64_encoded(
         self,
         **kwargs  # type: Any
     ):
-        # type: (...) -> bytes
+        # type: (...) -> bytearray
         """Get value that is base64 encoded.
 
         :keyword callable cls: A custom type or function that will be passed the direct response
-        :return: bytes, or the result of cls(response)
-        :rtype: bytes
+        :return: bytearray, or the result of cls(response)
+        :rtype: bytearray
         :raises: ~azure.core.exceptions.HttpResponseError
         """
-        cls = kwargs.pop('cls', None)  # type: ClsType[bytes]
+        cls = kwargs.pop('cls', None)  # type: ClsType[bytearray]
         error_map = {404: ResourceNotFoundError, 409: ResourceExistsError}
         error_map.update(kwargs.pop('error_map', {}))
 
@@ -497,7 +497,7 @@ def get_base64_encoded(
             error = self._deserialize(models.Error, response)
             raise HttpResponseError(response=response, model=error)
 
-        deserialized = self._deserialize('base64', pipeline_response)
+        deserialized = self._deserialize('bytearray', pipeline_response)
 
         if cls:
             return cls(pipeline_response, deserialized, {})