Fix not enough data in VSA

This commit fixes the not enough data message when 0 seconds are
returned from the median API by changing the data type to float.

changelogs/unreleased/202143-fix-not-enough-data-in-vsa.yml

+---
+title: Fix 'not enough data' in Value Stream Analytics when low median values are
+  returned
+merge_request: 31315
+author:
+type: fixed

lib/gitlab/analytics/cycle_analytics/median.rb

@@ -15,7 +15,7 @@ module Gitlab
           @query = @query.select(median_duration_in_seconds.as('median'))
           result = execute_query(@query).first || {}
 
-          result['median'] ? result['median'].to_i : nil
+          result['median'] || nil
         end
 
         def days

spec/lib/gitlab/analytics/cycle_analytics/median_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Gitlab::Analytics::CycleAnalytics::Median do
+  let_it_be(:project) { create(:project, :repository) }
+  let(:query) { Project.joins(merge_requests: :metrics) }
+
+  let(:stage) do
+    build(
+      :cycle_analytics_project_stage,
+      start_event_identifier: Gitlab::Analytics::CycleAnalytics::StageEvents::MergeRequestCreated.identifier,
+      end_event_identifier: Gitlab::Analytics::CycleAnalytics::StageEvents::MergeRequestMerged.identifier,
+      project: project
+    )
+  end
+
+  subject { described_class.new(stage: stage, query: query).seconds }
+
+  around do |example|
+    Timecop.freeze { example.run }
+  end
+
+  it 'retruns nil when no results' do
+    expect(subject).to eq(nil)
+  end
+
+  it 'returns median duration seconds as float' do
+    merge_request1 = create(:merge_request, source_branch: '1', target_project: project, source_project: project)
+    merge_request2 = create(:merge_request, source_branch: '2', target_project: project, source_project: project)
+
+    Timecop.travel(5.minutes.from_now) do
+      merge_request1.metrics.update!(merged_at: Time.zone.now)
+    end
+
+    Timecop.travel(10.minutes.from_now) do
+      merge_request2.metrics.update!(merged_at: Time.zone.now)
+    end
+
+    expect(subject).to be_within(0.5).of(7.5.minutes.seconds)
+  end
+end

spec/support/shared_examples/lib/gitlab/cycle_analytics/base_stage_shared_examples.rb

@@ -63,7 +63,7 @@ shared_examples 'Gitlab::Analytics::CycleAnalytics::DataCollector backend exampl
 
   context 'provides the same results as the old implementation' do
     it 'for the median' do
-      expect(data_collector.median.seconds).to eq(ISSUES_MEDIAN)
+      expect(data_collector.median.seconds).to be_within(0.5).of(ISSUES_MEDIAN)
     end
 
     it 'for the list of event records' do