Fail gracefully when config file is missing or bad

This is better than raising obscure exceptions from the internals.

lib/split/experiment.rb

@@ -157,6 +157,7 @@ def self.load_alternatives_for(name)
 
     def self.load_alternatives_from_configuration_for(name)
       alts = Split.configuration.experiment_for(name)[:variants]
+      raise ArgumentError, "Experiment configuration is missing :variants array" if alts.nil?
       if alts.is_a?(Hash)
         alts.keys
       else

spec/helper_spec.rb

@@ -649,6 +649,21 @@ def should_finish_experiment(experiment_name, should_finish=true)
       names_and_weights.should ==  [['control_opt', 0.18], ['second_opt', 0.18], ['third_opt', 0.64]]
       names_and_weights.inject(0){|sum, nw| sum + nw[1]}.should == 1.0
     end
+
+    it "fails gracefully if config is missing experiment" do
+      Split.configuration.experiments = { :other_experiment => { :foo => "Bar" } }
+      lambda { ab_test :my_experiment }.should raise_error(/not found/i)
+    end
+
+    it "fails gracefully if config is missing" do
+      Split.configuration.experiments = nil
+      lambda { ab_test :my_experiment }.should raise_error(/not found/i)
+    end
+
+    it "fails gracefully if config is missing variants" do
+      Split.configuration.experiments[:my_experiment] = { :foo => "Bar" }
+      lambda { ab_test :my_experiment }.should raise_error(/variants/i)
+    end
   end
 
   it 'should handle multiple experiments correctly' do