Add tests for question destroy use case

spec/lib/use_case/question/destroy_spec.rb

@@ -0,0 +1,47 @@
+# frozen_string_literal: true
+
+require "rails_helper"
+require "errors"
+require "use_case/question/destroy"
+
+describe UseCase::Question::Destroy do
+  subject do
+    UseCase::Question::Destroy.call(
+      question_id:  question.id,
+      current_user: current_user
+    )
+  end
+
+  shared_examples "deletes the question" do
+    it "deletes the question" do
+      expect { subject }.to change { Question.count }.by(-1)
+    end
+  end
+
+  context "question exists" do
+    let!(:question) { FactoryBot.create(:question, user: question_owner) }
+
+    context "user owns question" do
+      let(:question_owner) { FactoryBot.create(:user) }
+      let(:current_user) { question_owner }
+
+      it_behaves_like "deletes the question"
+    end
+
+    context "user is a moderator" do
+      let(:question_owner) { FactoryBot.create(:user) }
+      let(:current_user) { FactoryBot.create(:user, roles: [:moderator]) }
+
+      it_behaves_like "deletes the question"
+    end
+
+    context "user does not own question" do
+      let(:question_owner) { FactoryBot.create(:user) }
+      let(:current_user) { FactoryBot.create(:user) }
+
+      it "raises an error" do
+        expect { subject }.to raise_error(Errors::Forbidden)
+      end
+    end
+  end
+end