Move tracking behavior to configuration

- This improves usage patterns when using the Gitlab::Experiment base
class.

app/experiments/application_experiment.rb

@@ -32,17 +32,6 @@ class ApplicationExperiment < Gitlab::Experiment # rubocop:disable Gitlab/Namesp
     Experiment.add_subject(name, variant: variant || :control, subject: subject)
   end
 
-  def track(action, **event_args)
-    return unless should_track? # don't track events for excluded contexts
-
-    # track the event, and mix in the experiment signature data
-    Gitlab::Tracking.event(name, action.to_s, **event_args.merge(
-      context: (event_args[:context] || []) << SnowplowTracker::SelfDescribingJson.new(
-        'iglu:com.gitlab/gitlab_experiment/jsonschema/1-0-0', signature
-      )
-    ))
-  end
-
   def record!
     @record = true
   end

config/initializers/gitlab_experiment.rb

@@ -6,6 +6,13 @@ Gitlab::Experiment.configure do |config|
   config.cache = Gitlab::Experiment::Cache::RedisHashStore.new(
     pool: ->(&block) { Gitlab::Redis::SharedState.with { |redis| block.call(redis) } }
   )
+  config.tracking_behavior = lambda do |action, event_args|
+    Gitlab::Tracking.event(name, action.to_s, **event_args.merge(
+      context: (event_args[:context] || []) << SnowplowTracker::SelfDescribingJson.new(
+        'iglu:com.gitlab/gitlab_experiment/jsonschema/1-0-0', signature
+      )
+    ))
+  end
 end
 
 # TODO: This shim should be removed after the feature flag is rolled out, as

spec/experiments/application_experiment_spec.rb

@@ -150,6 +150,10 @@ RSpec.describe ApplicationExperiment, :experiment do
   end
 
   describe "#track", :snowplow do
+    let(:fake_context) do
+      SnowplowTracker::SelfDescribingJson.new('iglu:com.gitlab/fake/jsonschema/0-0-0', { data: '_data_' })
+    end
+
     it "doesn't track if we shouldn't track" do
       allow(subject).to receive(:should_track?).and_return(false)
 
@@ -159,9 +163,7 @@ RSpec.describe ApplicationExperiment, :experiment do
     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_' })
-      ])
+      subject.track(:action, property: '_property_', context: [fake_context])
 
       expect_snowplow_event(
         category: 'namespaced/stub',
@@ -179,6 +181,26 @@ RSpec.describe ApplicationExperiment, :experiment do
         ]
       )
     end
+
+    it "tracks the event correctly even when using the base class" do
+      subject = Gitlab::Experiment.new(:unnamed)
+      subject.track(:action, context: [fake_context])
+
+      expect_snowplow_event(
+        category: 'unnamed',
+        action: 'action',
+        context: [
+          {
+            schema: 'iglu:com.gitlab/fake/jsonschema/0-0-0',
+            data: { data: '_data_' }
+          },
+          {
+            schema: 'iglu:com.gitlab/gitlab_experiment/jsonschema/1-0-0',
+            data: { experiment: 'unnamed', key: subject.context.key, variant: 'control' }
+          }
+        ]
+      )
+    end
   end
 
   describe "#key_for" do