spec

lib/lab_coat/experiment.rb

@@ -73,6 +73,7 @@ def select_observation(result)
     end
 
     # Runs the control and candidate and publishes the result. Always returns the result of `control`.
+    # It's not recommended to override this method.
     # @param context [Hash] Any data needed at runtime.
     # @return [Object] An `Observation` value.
     def run!(**context) # rubocop:disable Metrics/MethodLength

test/test_experiment.rb

@@ -8,7 +8,7 @@ class TestExperiment < Minitest::Test
     attr_reader :raised_observations, :publish_io
 
     def enabled?
-      context[:num].even?
+      context[:num]&.even?
     end
 
     def control
@@ -42,6 +42,10 @@ def publishable_value(observation)
     def publish!(result)
       @publish_io = StringIO.new(JSON.generate(result.to_h))
     end
+
+    def select_observation(result)
+      context[:rollout] ? result.candidate : result.control
+    end
   end
 
   def setup
@@ -99,6 +103,25 @@ def test_publish!
     assert_match(/"experiment":"test-experiment"/, @experiment.publish_io.read)
   end
 
+  def test_select_observation # rubocop:disable Metrics/MethodLength
+    # Returns control even if rollout is true if not enabled.
+    assert_equal(
+      { result: "abc", status: :ok },
+      @experiment.run!(rollout: true)
+    )
+
+    # Returns control if rollout is false, even if enabled.
+    assert_equal(
+      { result: "abc", status: :ok },
+      @experiment.run!(rollout: false, num: 2)
+    )
+
+    # Returns candidate when rollout is true and is enabled.
+    assert_nil(
+      @experiment.run!(rollout: true, num: 2)
+    )
+  end
+
   def test_run!
     assert_equal(
       { result: "abc", status: :ok },