Add (an admittedly contrived) failing spec for conditionally shared data

spec/dummy/app/controllers/inertia_conditional_sharing_controller.rb

@@ -0,0 +1,22 @@
+class InertiaConditionalSharingController < ApplicationController
+  before_action :conditionally_share_props, only: [:show]
+  inertia_share normal_shared_prop: 1
+
+  def index
+    render inertia: 'EmptyTestComponent', props: {
+      index_only_prop: 1,
+    }
+  end
+
+  def show
+    render inertia: 'EmptyTestComponent', props: {
+      show_only_prop: 1,
+    }
+  end
+
+  protected
+
+  def conditionally_share_props
+    self.class.inertia_share conditionally_shared_show_prop: 1
+  end
+end

spec/dummy/config/routes.rb

@@ -45,4 +45,7 @@
   get 'merge_instance_props' => 'inertia_merge_instance_props#merge_instance_props'
 
   get 'lamda_shared_props' => 'inertia_lambda_shared_props#lamda_shared_props'
+
+  get 'conditional_share_index' => 'inertia_conditional_sharing#index'
+  get 'conditional_share_show' => 'inertia_conditional_sharing#show'
 end

spec/inertia/conditional_sharing_spec.rb

@@ -0,0 +1,26 @@
+RSpec.describe "conditionally shared data in a controller", type: :request do
+  it 'does not leak data between requests' do
+    get conditional_share_index_path, headers: {'X-Inertia' => true}
+    expect(JSON.parse(response.body)['props'].deep_symbolize_keys).to eq({
+      index_only_prop: 1,
+      normal_shared_prop: 1,
+    })
+
+    # NOTE: we actually have to run the show action twice since the new implementation
+    # sets up a before_action within a before_action to share the data.
+    # In effect, that means that the shared data isn't rendered until the second time the action is run.
+    get conditional_share_show_path, headers: {'X-Inertia' => true}
+    get conditional_share_show_path, headers: {'X-Inertia' => true}
+    expect(JSON.parse(response.body)['props'].deep_symbolize_keys).to eq({
+      normal_shared_prop: 1,
+      show_only_prop: 1,
+      conditionally_shared_show_prop: 1,
+    })
+
+    get conditional_share_index_path, headers: {'X-Inertia' => true}
+    expect(JSON.parse(response.body)['props'].deep_symbolize_keys).to eq({
+      index_only_prop: 1,
+      normal_shared_prop: 1,
+    })
+  end
+end