Feature: Global Config helper (#844) (#845)

* Added a global config helper to easily access installation/global configs
  * this will fetch the keys from cache with fallback to DB on cache miss
  * ability to query multiple keys simultaneously
  * interface to delete the existing global config cache
* Added tests for this new helper module

spec/lib/global_config_spec.rb

@@ -0,0 +1,39 @@
+require 'rails_helper'
+
+describe GlobalConfig do
+  subject(:trigger) { described_class }
+
+  describe 'execute' do
+    context 'when called with default options' do
+      before do
+        described_class.clear_cache
+      end
+
+      it 'hit DB for the first call' do
+        expect(InstallationConfig).to receive(:find_by)
+        described_class.get('test')
+      end
+
+      it 'get from cache for subsequent calls' do
+        # this loads from DB
+        described_class.get('test')
+
+        # subsequent calls should not hit DB
+        expect(InstallationConfig).not_to receive(:find_by)
+        described_class.get('test')
+      end
+
+      it 'clears cache and fetch from DB next time, when clear_cache is called' do
+        # this loads from DB and is cached
+        described_class.get('test')
+
+        # clears the cache
+        described_class.clear_cache
+
+        # should be loaded from DB
+        expect(InstallationConfig).to receive(:find_by).with({ name: 'test' }).and_return(nil)
+        described_class.get('test')
+      end
+    end
+  end
+end