Added user qualification functionality

Author: robin-phung

Diff for: lib/split/helper.rb

@@ -11,9 +11,13 @@ def ab_test(metric_descriptor, control = nil, *alternatives)
         alternative = if Split.configuration.enabled && !exclude_visitor?
           experiment.save
           raise(Split::InvalidExperimentsFormatError) unless (Split.configuration.experiments || {}).fetch(experiment.name.to_sym, {})[:combined_experiments].nil?
-          trial = Trial.new(:user => ab_user, :experiment => experiment,
-              :override => override_alternative(experiment.name), :exclude => exclude_visitor?,
-              :disabled => split_generically_disabled?)
+          trial = Trial.new(
+            :user => ab_user, 
+            :experiment => experiment,
+            :override => override_alternative(experiment.name), 
+            :exclude => !is_qualified?,
+            :disabled => split_generically_disabled?
+          )
           alt = trial.choose!(self)
           alt ? alt.name : nil
         else
@@ -161,5 +165,11 @@ def normalize_metric(metric_descriptor)
     def control_variable(control)
       Hash === control ? control.keys.first.to_s : control.to_s
     end
+
+    private 
+    
+    def is_qualified?
+      self.respond_to?(:ab_test_user_qualified?, true) ? self.send(:ab_test_user_qualified?) : true
+    end
   end
 end

Diff for: spec/helper_spec.rb

@@ -274,6 +274,30 @@
       ab_test('link_color', 'blue', 'red')
       expect(ab_user).to eq(finished_session)
     end
+
+    context "with ab_test_user_qualified is set" do
+      context "ab_test_user_qualified returns true" do
+        def ab_test_user_qualified?
+          true 
+        end
+ 
+        it "user is qualified to participate in experiment" do
+          ab_test('link_color', 'blue', 'red')
+          expect(['red', 'blue']).to include(ab_user['link_color'])
+        end
+      end
+
+      context "ab_test_user_qualified returns false" do
+        def ab_test_user_qualified?
+          false 
+        end
+
+        it "user is not qualified to participate in experiment" do
+          ab_test('link_color', 'blue', 'red')
+          expect(ab_user['link_color']).to eq(nil)
+        end
+      end
+    end
   end
 
   describe 'metadata' do