fix: Add context_data attribute to _MonkeyPatchedW/ASGIResponse. (#2509)

As detailed in Django's documentation [0], when a non-standard template backend is being used, the `context_data` attribute is populated instead of `context` when the test API call was successful. In reality, I've seen this to be a populated attribute regardless of the backend template engine being used. Regardless, this near hidden attribute is missing and should be included to help improve unit testing when validating the response data contains the expected data.

Author: PacificGilly

django-stubs/test/client.pyi

@@ -189,7 +189,15 @@ class _MonkeyPatchedWSGIResponse(_WSGIResponse):
     request: dict[str, Any]
     client: Client
     templates: list[Template]
+
+    # `context` and `context_data` are populated based on whether you use the standard template
+    # backend or a custom one respectively.
+    # `context_data` only exists if the response was successful too as the return type changes.
+    # `HTTPResponse` when API failed and `TemplateResponse` when successful.
+    # https://docs.djangoproject.com/en/stable/topics/testing/tools/#django.test.Response.context
     context: ContextList | dict[str, Any]
+    context_data: ContextList | dict[str, Any]
+
     content: bytes
     resolver_match: ResolverMatch
     redirect_chain: list[tuple[str, int]]
@@ -200,7 +208,15 @@ class _MonkeyPatchedASGIResponse(_ASGIResponse):
     request: dict[str, Any]
     client: AsyncClient
     templates: list[Template]
+
+    # `context` and `context_data` are populated based on whether you use the standard template
+    # backend or a custom one respectively.
+    # `context_data` only exists if the response was successful too as the return type changes.
+    # `HTTPResponse` when API failed and `TemplateResponse` when successful.
+    # https://docs.djangoproject.com/en/stable/topics/testing/tools/#django.test.Response.context
     context: ContextList | dict[str, Any]
+    context_data: ContextList | dict[str, Any]
+
     content: bytes
     resolver_match: ResolverMatch
     redirect_chain: list[tuple[str, int]]

tests/typecheck/test/test_client.yml

@@ -8,6 +8,7 @@
       reveal_type(response.templates)  # N: Revealed type is "builtins.list[django.template.base.Template]"
       reveal_type(response.client)  # N: Revealed type is "django.test.client.Client"
       reveal_type(response.context)  # N: Revealed type is "Union[django.test.utils.ContextList, builtins.dict[builtins.str, Any]]"
+      reveal_type(response.context_data)  # N: Revealed type is "Union[django.test.utils.ContextList, builtins.dict[builtins.str, Any]]"
       reveal_type(response.content)  # N: Revealed type is "builtins.bytes"
       reveal_type(response.redirect_chain)  # N: Revealed type is "builtins.list[Tuple[builtins.str, builtins.int]]"
       response.json()
@@ -22,6 +23,7 @@
         reveal_type(response.templates)  # N: Revealed type is "builtins.list[django.template.base.Template]"
         reveal_type(response.client)  # N: Revealed type is "django.test.client.AsyncClient"
         reveal_type(response.context)  # N: Revealed type is "Union[django.test.utils.ContextList, builtins.dict[builtins.str, Any]]"
+        reveal_type(response.context_data)  # N: Revealed type is "Union[django.test.utils.ContextList, builtins.dict[builtins.str, Any]]"
         reveal_type(response.content)  # N: Revealed type is "builtins.bytes"
         reveal_type(response.redirect_chain)  # N: Revealed type is "builtins.list[Tuple[builtins.str, builtins.int]]"
         response.json()