Migrate configuration into ApplicationExperiment

- This makes the configuration easier to test, improves those tests, and
provides a base class that all future experiments can use.

app/experiments/application_experiment.rb

+# frozen_string_literal: true
+
+class ApplicationExperiment < Gitlab::Experiment
+  def publish(_result)
+    track(:assignment) # track that we've assigned a variant for this context
+    Gon.global.push({ experiment: { name => signature } }, true) # push to client
+  end
+
+  def track(action, **event_args)
+    return if excluded? # no events for opted out actors or excluded subjects
+
+    Gitlab::Tracking.event(name, action.to_s, **event_args.merge(
+      context: (event_args[:context] || []) << SnowplowTracker::SelfDescribingJson.new(
+        'iglu:com.gitlab/gitlab_experiment/jsonschema/0-3-0', signature
+      )
+    ))
+  end
+
+  private
+
+  def resolve_variant_name
+    variant_names.first if Feature.enabled?(name, self, type: :experiment)
+  end
+end

config/initializers/gitlab_experiment.rb

 # frozen_string_literal: true
 
 Gitlab::Experiment.configure do |config|
-  # Logic this project uses to resolve a variant for a given experiment.
-  #
-  # This can return an instance of any object that responds to `name`, or can
-  # return a variant name as a symbol or string.
-  #
-  # This block will be executed within the scope of the experiment instance,
-  # so can easily access experiment methods, like getting the name or context.
-  config.variant_resolver = lambda do |requested_variant|
-    # Return the variant if one was requested in code:
-    break requested_variant if requested_variant.present?
-
-    # Use Feature interface to determine the variant by passing the experiment,
-    # which responds to `flipper_id` and `session_id` to accommodate adapters.
-    variant_names.first if Feature.enabled?(name, self, type: :experiment)
-  end
-
-  # Tracking behavior can be implemented to link an event to an experiment.
-  #
-  # Similar to the variant_resolver, this is called within the scope of the
-  # experiment instance and so can access any methods on the experiment,
-  # such as name and signature.
-  config.tracking_behavior = lambda do |event, args|
-    Gitlab::Tracking.event(name, event.to_s, **args.merge(
-      context: (args[:context] || []) << SnowplowTracker::SelfDescribingJson.new(
-        'iglu:com.gitlab/gitlab_experiment/jsonschema/0-3-0', signature
-      )
-    ))
-  end
-
-  # Called at the end of every experiment run, with the result.
-  #
-  # You may want to track that you've assigned a variant to a given context,
-  # or push the experiment into the client or publish results elsewhere, like
-  # into redis or postgres. Also called within the scope of the experiment
-  # instance.
-  config.publishing_behavior = lambda do |result|
-    # Track the event using our own configured tracking logic.
-    track(:assignment)
-
-    # Push the experiment knowledge into the front end. The signature contains
-    # the context key, and the variant that has been determined.
-    Gon.push({ experiment: { name => signature } }, true)
-  end
+  config.base_class = 'ApplicationExperiment'
 end

lib/quality/test_level.rb

@@ -23,6 +23,7 @@ module Quality
         dependencies
         elastic
         elastic_integration
+        experiments
         factories
         finders
         frontend

spec/experiments/application_experiment_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe ApplicationExperiment do
+  subject { described_class.new(:stub) }
+
+  describe "publishing results" do
+    it "tracks the assignment" do
+      expect(subject).to receive(:track).with(:assignment)
+
+      subject.publish(nil)
+    end
+
+    it "pushes the experiment knowledge into the client using Gon.global" do
+      expect(Gon.global).to receive(:push).with(
+        {
+          experiment: {
+            'stub' => { # string key because it can be namespaced
+              experiment: 'stub',
+              key: 'e8f65fd8d973f9985dc7ea3cf1614ae1',
+              variant: 'control'
+            }
+          }
+        },
+        true
+      )
+
+      subject.publish(nil)
+    end
+  end
+
+  describe "tracking events", :snowplow do
+    before do
+      allow(Gitlab::Tracking).to receive(:event)
+    end
+
+    it "doesn't track if excluded" do
+      subject.exclude { true }
+
+      subject.track(:action)
+
+      expect_no_snowplow_event
+    end
+
+    it "tracks the event with the expected arguments and merged contexts" do
+      subject.track(:action, property: '_property_', context: [
+        SnowplowTracker::SelfDescribingJson.new('iglu:com.gitlab/fake/jsonschema/0-0-0', { data: '_data_' })
+      ])
+
+      expect_snowplow_event(
+        category: 'stub',
+        action: 'action',
+        property: '_property_',
+        context: [
+          {
+            schema: 'iglu:com.gitlab/fake/jsonschema/0-0-0',
+            data: { data: '_data_' }
+          },
+          {
+            schema: 'iglu:com.gitlab/gitlab_experiment/jsonschema/0-3-0',
+            data: { experiment: 'stub', key: 'e8f65fd8d973f9985dc7ea3cf1614ae1', variant: 'control' }
+          }
+        ]
+      )
+    end
+  end
+
+  describe "variant resolution" do
+    it "returns nil when not rolled out" do
+      stub_feature_flags(stub: false)
+
+      expect(subject.variant.name).to eq('control')
+    end
+
+    context "when the rollout out to 100%" do
+      it "returns the first variant name" do
+        subject.try(:variant1) {}
+        subject.try(:variant2) {}
+
+        expect(subject.variant.name).to eq('variant1')
+      end
+    end
+  end
+end