Add RedisHllGenerator specs

spec/lib/generators/gitlab/usage_metric_definition/redis_hll_generator_spec.rb

+# frozen_string_literal: true
+
+require 'generator_helper'
+
+RSpec.describe Gitlab::UsageMetricDefinition::RedisHllGenerator do
+  let(:category) { 'test_category' }
+  let(:event) { 'i_test_event' }
+  let(:args) { [category, event] }
+  let(:temp_dir) { Dir.mktmpdir }
+
+  # Interpolating to preload the class
+  # See https://github.com/rspec/rspec-mocks/issues/1079
+  before do
+    stub_const("#{Gitlab::UsageMetricDefinitionGenerator}::TOP_LEVEL_DIR", temp_dir)
+  end
+
+  it 'creates metric definition files' do
+    described_class.new(args).invoke_all
+
+    weekly_metric_definition_path = Dir.glob(File.join(temp_dir, 'metrics/counts_7d/*i_test_event.yml')).first
+    monthly_metric_definition_path = Dir.glob(File.join(temp_dir, 'metrics/counts_28d/*i_test_event.yml')).first
+
+    expect(YAML.safe_load(File.read(weekly_metric_definition_path))).to include("key_path" => "redis_hll_counters.test_category.i_test_event")
+    expect(YAML.safe_load(File.read(monthly_metric_definition_path))).to include("key_path" => "redis_hll_counters.test_category.i_test_event")
+  end
+end