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

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

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+# 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)