1 files changed, 60 insertions, 0 deletions
diff --git a/spec/services/topics/merge_service_spec.rb b/spec/services/topics/merge_service_spec.rb
new file mode 100644
index 00000000000..971917eb8e9
--- /dev/null
+++ b/spec/services/topics/merge_service_spec.rb
@@ -0,0 +1,60 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Topics::MergeService do
+  let_it_be(:source_topic) { create(:topic, name: 'source_topic') }
+  let_it_be(:target_topic) { create(:topic, name: 'target_topic') }
+  let_it_be(:project_1) { create(:project, :public, topic_list: source_topic.name ) }
+  let_it_be(:project_2) { create(:project, :private, topic_list: source_topic.name ) }
+  let_it_be(:project_3) { create(:project, :public, topic_list: target_topic.name ) }
+  let_it_be(:project_4) { create(:project, :public, topic_list: [source_topic.name, target_topic.name] ) }
+
+  subject { described_class.new(source_topic, target_topic).execute }
+
+  describe '#execute' do
+    it 'merges source topic into target topic' do
+      subject
+
+      expect(target_topic.projects).to contain_exactly(project_1, project_2, project_3, project_4)
+      expect { source_topic.reload }.to raise_error(ActiveRecord::RecordNotFound)
+    end
+
+    it 'refreshes counters of target topic' do
+      expect { subject }
+        .to change { target_topic.reload.total_projects_count }.by(2)
+        .and change { target_topic.reload.non_private_projects_count }.by(1)
+    end
+
+    context 'when source topic fails to delete' do
+      it 'reverts previous changes' do
+        allow(source_topic.reload).to receive(:destroy!).and_raise(ActiveRecord::RecordNotDestroyed)
+
+        expect { subject }.to raise_error(ActiveRecord::RecordNotDestroyed)
+
+        expect(source_topic.projects).to contain_exactly(project_1, project_2, project_4)
+        expect(target_topic.projects).to contain_exactly(project_3, project_4)
+      end
+    end
+
+    context 'for parameter validation' do
+      using RSpec::Parameterized::TableSyntax
+
+      subject { described_class.new(source_topic_parameter, target_topic_parameter).execute }
+
+      where(:source_topic_parameter, :target_topic_parameter, :expected_message) do
+        nil                | ref(:target_topic) | 'The source topic is not a topic.'
+        ref(:source_topic) | nil                | 'The target topic is not a topic.'
+        ref(:target_topic) | ref(:target_topic) | 'The source topic and the target topic are identical.' # rubocop:disable Lint/BinaryOperatorWithIdenticalOperands
+      end
+
+      with_them do
+        it 'raises correct error' do
+          expect { subject }.to raise_error(ArgumentError) do |error|
+            expect(error.message).to eq(expected_message)
+          end
+        end
+      end
+    end
+  end
+end