fix user participating alternative not found (#536)

Author: NaturalHokke

lib/split/trial.rb

@@ -68,10 +68,8 @@ def choose!(context = nil)
         if exclude_user?
           self.alternative = @experiment.control
         else
-          value = @user[@experiment.key]
-          if value
-            self.alternative = value
-          else
+          self.alternative = @user[@experiment.key]
+          if alternative.nil?
             self.alternative = @experiment.next_alternative
 
             # Increment the number of participants since we are actually choosing a new alternative

spec/trial_spec.rb

@@ -176,6 +176,14 @@ def expect_alternative(trial, alternative_name)
 
         expect_alternative(trial, 'basket')
       end
+
+      context "when alternative is not found" do
+        it "falls back on next_alternative" do
+          user[experiment.key] = 'notfound'
+          expect(experiment).to receive(:next_alternative).and_call_original
+          expect_alternative(trial, alternatives)
+        end
+      end
     end
 
     context "when user is a new participant" do