grab experiment-group metrics nicely with exp.metrics(:group)

lib/modesty/experiment.rb

@@ -1,5 +1,7 @@
 module Modesty
   class Experiment
+    class Error < StandardError; end
+
     class Builder
       def method_missing(name, *args)
         if Experiment::ATTRIBUTES.include?(name) && args.count > 0
@@ -69,8 +71,17 @@ def alternatives
       @alternatives ||= [:control, :experiment]
     end
 
-    def metrics
+    def metrics(alt=nil)
       @metrics ||= []
+      return @metrics unless alt
+      raise Error, <<-msg.squish unless self.alternatives.include? alt
+        Unrecognized alternative #{alt.inspect} for #{self.inspect}.
+        Available alternatives: #{self.alternatives.inspect}
+      msg
+
+      Hash[@metrics.map do |m|
+        [m.slug, m/(self.slug/alt)]
+      end]
     end
 
     def data
@@ -132,11 +143,12 @@ def users(alt=nil)
   end
 
   module ExperimentMethods
-    attr_accessor :experiments
+    def experiments
+      @experiments ||= {}
+    end
 
     def add_experiment(exp)
-      @experiments ||= {}
-      raise "Experiment already defined!" if @experiments[exp.slug]
+      raise Error, "Experiment already defined!" if @experiments[exp.slug]
       @experiments[exp.slug] = exp
     end
 

spec/experiment_spec.rb

@@ -52,6 +52,19 @@
     Modesty.metrics.keys.should include :baz/:ab_test/:control
     Modesty.metrics.keys.should include :baz/:ab_test/:experiment
   end
+
+  it "grabs metrics nicely with e.metrics(alt)" do
+    @e.alternatives.each do |alt|
+      @e.metrics(alt).should == {
+        :foo/:bar => Modesty.metrics[:foo/:bar/:creation_page/alt],
+        :baz      => Modesty.metrics[:baz/:creation_page/alt],
+      }
+    end
+
+    lambda do
+      @e.metrics(:i_dont_exist)
+    end.should raise_error(Modesty::Experiment::Error)
+  end
 end
 
 describe "A/B testing" do