Add Mock Rails Environment With An Inquiry Instance as a Rails TIL

README.md

@@ -10,7 +10,7 @@ pairing with smart people at Hashrocket.
 
 For a steady stream of TILs, [sign up for my newsletter](https://crafty-builder-6996.ck.page/e169c61186).
 
-_1335 TILs and counting..._
+_1336 TILs and counting..._
 
 ---
 
@@ -848,6 +848,7 @@ _1335 TILs and counting..._
 - [Mask An ActiveRecord Attribute](rails/mask-an-activerecord-attribute.md)
 - [Merge A Scope Into An ActiveRecord Query](rails/merge-a-scope-into-an-activerecord-query.md)
 - [Migrating Up Down Up](rails/migrating-up-down-up.md)
+- [Mock Rails Environment With An Inquiry Instance](rails/mock-rails-environment-with-an-inquiry-instance.md)
 - [Order Matters For `rescue_from` Blocks](rails/order-matters-for-rescue-from-blocks.md)
 - [Params Includes Submission Button Info](rails/params-includes-submission-button-info.md)
 - [Params Is A Hash With Indifferent Access](rails/params-is-a-hash-with-indifferent-access.md)

rails/mock-rails-environment-with-an-inquiry-instance.md

@@ -0,0 +1,38 @@
+# Mock Rails Environment With An Inquiry Instance
+
+As discussed in [Make A String Attribute Easy to Inquire
+About](make-a-string-attribute-easy-to-inquire-about.md), the `Rails.env` is
+assigned an instance of `ActiveSupport::StringInquirer`. This allows us to ask
+whether the current Rails environment is `#production?`, `#development?`, etc.
+
+With this in mind, we can have a test execute in a specific environment by
+mocking how `Rails.env` responds. Though the actual env for a test is going to
+be `test`, we can simulate a different environment with an RSpec `before` block
+like the following:
+
+```ruby
+before do
+  allow(Rails).to receive(:env) { "staging".inquiry }
+end
+```
+
+Or similarly, to simulate the `production` environment:
+
+```ruby
+before do
+  allow(Rails).to receive(:env) { "production".inquiry }
+end
+```
+
+The `#inquiry` being monkey-patched onto the `String` class gives you the
+willies, you could do the following instead:
+
+```ruby
+before do
+  allow(Rails).to receive(:env) do
+    ActiveSupport::StringInquirer.new("production")
+  end
+end
+```
+
+[source](https://stackoverflow.com/a/25134591/535590)