Merge pull request #46599 from shouichi/improve-active-storage-guide

Describe env specific ActiveStorage config in the AS guide [skip ci]

guides/source/active_storage_overview.md

@@ -113,9 +113,6 @@ To use the test service when testing, you add the following to
 config.active_storage.service = :test
 ```
 
-Continue reading for more information on the built-in service adapters (e.g.
-`Disk` and `S3`) and the configuration they require.
-
 NOTE: Configuration files that are environment-specific will take precedence:
 in production, for example, the `config/storage/production.yml` file (if existent)
 will take precedence over the `config/storage.yml` file.
@@ -139,6 +136,9 @@ azure:
   container: your_container_name-<%= Rails.env %>
 ```
 
+Continue reading for more information on the built-in service adapters (e.g.
+`Disk` and `S3`) and the configuration they require.
+
 ### Disk Service
 
 Declare a Disk service in `config/storage.yml`:
@@ -1415,6 +1415,33 @@ end
 [fixtures]: testing.html#the-low-down-on-fixtures
 [`ActiveStorage::FixtureSet`]: https://api.rubyonrails.org/classes/ActiveStorage/FixtureSet.html
 
+### Configuring services
+
+You can add `config/storage/test.yml` to configure services to be used in test environment
+This is useful when the `service` option is used.
+
+```ruby
+class User < ApplicationRecord
+  has_one_attached :avatar, service: :s3
+end
+```
+
+Without `config/storage/test.yml`, the `s3` service configured in `config/storage.yml` is used - even when running tests.
+
+The default configuration would be used and files would be uploaded to the service provider configured in `config/storage.yml`.
+
+In this case, you can add `config/storage/test.yml` and use Disk service for `s3` service to prevent sending requests.
+
+```yaml
+test:
+  service: Disk
+  root: <%= Rails.root.join("tmp/storage") %>
+
+s3:
+  service: Disk
+  root: <%= Rails.root.join("tmp/storage") %>
+```
+
 Implementing Support for Other Cloud Services
 ---------------------------------------------