1 files changed, 121 insertions, 0 deletions
diff --git a/spec/support_specs/database/multiple_databases_helpers_spec.rb b/spec/support_specs/database/multiple_databases_helpers_spec.rb
new file mode 100644
index 00000000000..eb0e980d376
--- /dev/null
+++ b/spec/support_specs/database/multiple_databases_helpers_spec.rb
@@ -0,0 +1,121 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe 'Database::MultipleDatabasesHelpers' do
+  let(:query) do
+    <<~SQL
+      WITH cte AS #{Gitlab::Database::AsWithMaterialized.materialized_if_supported} (SELECT 1) SELECT 1;
+    SQL
+  end
+
+  it 'preloads database version for ApplicationRecord' do
+    counts = ActiveRecord::QueryRecorder
+    .new { ApplicationRecord.connection.execute(query) }
+    .count
+
+    expect(counts).to eq(1)
+  end
+
+  it 'preloads database version for Ci::ApplicationRecord' do
+    counts = ActiveRecord::QueryRecorder
+    .new { Ci::ApplicationRecord.connection.execute(query) }
+    .count
+
+    expect(counts).to eq(1)
+  end
+
+  describe '.with_reestablished_active_record_base' do
+    context 'when doing establish_connection' do
+      context 'on ActiveRecord::Base' do
+        it 'raises exception' do
+          expect { ActiveRecord::Base.establish_connection(:main) }.to raise_error /Cannot re-establish/ # rubocop: disable Database/EstablishConnection
+        end
+
+        context 'when using with_reestablished_active_record_base' do
+          it 'does not raise exception' do
+            with_reestablished_active_record_base do
+              expect { ActiveRecord::Base.establish_connection(:main) }.not_to raise_error # rubocop: disable Database/EstablishConnection
+            end
+          end
+        end
+      end
+
+      context 'on Ci::ApplicationRecord' do
+        before do
+          skip_if_multiple_databases_not_setup
+        end
+
+        it 'raises exception' do
+          expect { Ci::ApplicationRecord.establish_connection(:ci) }.to raise_error /Cannot re-establish/ # rubocop: disable Database/EstablishConnection
+        end
+
+        context 'when using with_reestablished_active_record_base' do
+          it 'does not raise exception' do
+            with_reestablished_active_record_base do
+              expect { Ci::ApplicationRecord.establish_connection(:main) }.not_to raise_error # rubocop: disable Database/EstablishConnection
+            end
+          end
+        end
+      end
+    end
+
+    context 'when trying to access connection' do
+      context 'when reconnect is true' do
+        it 'does not raise exception' do
+          with_reestablished_active_record_base(reconnect: true) do
+            expect { ApplicationRecord.connection.execute("SELECT 1") }.not_to raise_error
+          end
+        end
+      end
+
+      context 'when reconnect is false' do
+        it 'does raise exception' do
+          with_reestablished_active_record_base(reconnect: false) do
+            expect { ApplicationRecord.connection.execute("SELECT 1") }
+              .to raise_error(ActiveRecord::ConnectionNotEstablished)
+          end
+        end
+      end
+    end
+  end
+
+  describe '.with_added_ci_connection' do
+    context 'when only a single database is setup' do
+      before do
+        skip_if_multiple_databases_are_setup
+      end
+
+      it 'connects Ci::ApplicationRecord to the main database for the duration of the block', :aggregate_failures do
+        main_database = current_database(ActiveRecord::Base)
+        original_database = current_database(Ci::ApplicationRecord)
+
+        with_added_ci_connection do
+          expect(current_database(Ci::ApplicationRecord)).to eq(main_database)
+        end
+
+        expect(current_database(Ci::ApplicationRecord)).to eq(original_database)
+      end
+    end
+
+    context 'when multiple databases are setup' do
+      before do
+        skip_if_multiple_databases_not_setup
+      end
+
+      it 'does not mock the original Ci::ApplicationRecord connection', :aggregate_failures do
+        original_database = current_database(Ci::ApplicationRecord)
+
+        with_added_ci_connection do
+          expect(current_database(Ci::ApplicationRecord)).to eq(original_database)
+        end
+
+        expect(current_database(Ci::ApplicationRecord)).to eq(original_database)
+      end
+    end
+
+    def current_database(connection_class)
+      connection_class.retrieve_connection.execute('select current_database()').first
+    end
+  end
+end