Add tests for synchronizing all execution environments

This adds policy tests to ensure only an admin can synchronize all
execution environments. It also adds controller tests that check that
all execution environments get synchronized.

spec/controllers/execution_environments_controller_spec.rb

@@ -192,4 +192,20 @@ describe ExecutionEnvironmentsController do
       end
     end
   end
+
+  describe '#synchronize_all_to_poseidon' do
+    let(:execution_environments) { FactoryBot.build_list(:ruby, 3) }
+
+    it 'copies all execution environments to Poseidon' do
+      allow(ExecutionEnvironment).to receive(:all).and_return(execution_environments)
+
+      execution_environments.each do |execution_environment|
+        allow(execution_environment).to receive(:copy_to_poseidon).and_return(true)
+      end
+
+      post :synchronize_all_to_poseidon
+
+      expect(execution_environments).to all(have_received(:copy_to_poseidon).once)
+    end
+  end
 end