1 files changed, 39 insertions, 0 deletions
diff --git a/spec/lib/gitlab/database/migrations/observers/total_database_size_change_spec.rb b/spec/lib/gitlab/database/migrations/observers/total_database_size_change_spec.rb
new file mode 100644
index 00000000000..73466471944
--- /dev/null
+++ b/spec/lib/gitlab/database/migrations/observers/total_database_size_change_spec.rb
@@ -0,0 +1,39 @@
+# frozen_string_literal: true
+require 'spec_helper'
+
+RSpec.describe Gitlab::Database::Migrations::Observers::TotalDatabaseSizeChange do
+  subject { described_class.new }
+
+  let(:observation) { Gitlab::Database::Migrations::Observation.new }
+  let(:connection) { ActiveRecord::Base.connection }
+  let(:query) { 'select pg_database_size(current_database())' }
+
+  it 'records the size change' do
+    expect(connection).to receive(:execute).with(query).once.and_return([{ 'pg_database_size' => 1024 }])
+    expect(connection).to receive(:execute).with(query).once.and_return([{ 'pg_database_size' => 256 }])
+
+    subject.before
+    subject.after
+    subject.record(observation)
+
+    expect(observation.total_database_size_change).to eq(256 - 1024)
+  end
+
+  context 'out of order calls' do
+    before do
+      allow(connection).to receive(:execute).with(query).and_return([{ 'pg_database_size' => 1024 }])
+    end
+
+    it 'does not record anything if before size is unknown' do
+      subject.after
+
+      expect { subject.record(observation) }.not_to change { observation.total_database_size_change }
+    end
+
+    it 'does not record anything if after size is unknown' do
+      subject.before
+
+      expect { subject.record(observation) }.not_to change { observation.total_database_size_change }
+    end
+  end
+end