Provide an option to generically disable Split.

README.mdown

@@ -179,6 +179,12 @@ If you have an experiment called `button_color` with alternatives called `red` a
 
 will always have red buttons. This won't be stored in your session or count towards to results, unless you set the `store_override` configuration option.
 
+In the event you want to disable all tests without having to know the individual experiment names, add a `SPLIT_DISABLE` query parameter.
+
+    http://myawesomesite.com?SPLIT_DISABLE=trues
+
+It is not required to send `SPLIT_DISABLE=false` to activate Split.
+
 ### Starting experiments manually
 
 By default new AB tests will be active right after deployment. In case you would like to start new test a while after

lib/split/helper.rb

@@ -31,8 +31,9 @@ def ab_test(metric_descriptor, control=nil, *alternatives)
         raise(e) unless Split.configuration.db_failover
         Split.configuration.db_failover_on_db_error.call(e)
 
-        if Split.configuration.db_failover_allow_parameter_override && override_present?(experiment_name)
-          ret = override_alternative(experiment_name)
+        if Split.configuration.db_failover_allow_parameter_override
+          ret = override_alternative(experiment_name) if override_present?(experiment_name)
+          ret = control_variable(control) if split_generically_disabled?
         end
       ensure
         ret ||= control_variable(control)
@@ -97,6 +98,10 @@ def override_alternative(experiment_name)
       params[experiment_name] if override_present?(experiment_name)
     end
 
+    def split_generically_disabled?
+      defined?(params) && params['SPLIT_DISABLE']
+    end
+
     def begin_experiment(experiment, alternative_name = nil)
       alternative_name ||= experiment.control.name
       ab_user[experiment.key] = alternative_name
@@ -169,6 +174,9 @@ def start_trial(trial)
       if override_present?(experiment.name) and experiment[override_alternative(experiment.name)]
         ret = override_alternative(experiment.name)
         ab_user[experiment.key] = ret if Split.configuration.store_override
+      elsif split_generically_disabled?
+        ret = experiment.control.name
+        ab_user[experiment.key] = ret if Split.configuration.store_override
       elsif experiment.has_winner?
         ret = experiment.winner.name
       else

spec/helper_spec.rb

@@ -113,6 +113,24 @@
       ab_test('link_color', 'blue', 'red')
     end
 
+    it "SPLIT_DISABLE query parameter should also force the alternative (uses control)" do
+      @params = {'SPLIT_DISABLE' => 'true'}
+      alternative = ab_test('link_color', 'blue', 'red')
+      alternative.should eql('blue')
+      alternative = ab_test('link_color', {'blue' => 1}, 'red' => 5)
+      alternative.should eql('blue')
+      alternative = ab_test('link_color', 'red', 'blue')
+      alternative.should eql('red')
+      alternative = ab_test('link_color', {'red' => 5}, 'blue' => 1)
+      alternative.should eql('red')
+    end
+
+    it "should not store the split when Split generically disabled" do
+      @params = {'SPLIT_DISABLE' => 'true'}
+      ab_user.should_not_receive(:[]=)
+      ab_test('link_color', 'blue', 'red')
+    end
+
     context "when store_override is set" do
       before { Split.configuration.store_override = true }