Create rspec test case for existing fix

Create rspec test case for existing fix

for commit 3731c713ab978aa46d4693fb79e0b927d280e3b3

diff --git a/spec/lib/internal_metric/custom_spec.rb b/spec/lib/internal_metric/custom_spec.rb
new file mode 100644
index 0000000..ae1fc62
--- /dev/null
+++ b/spec/lib/internal_metric/custom_spec.rb
@@ -0,0 +1,22 @@
+require 'rails_helper'
+
+module DiscoursePrometheus::InternalMetric
+  describe Custom do
+    it "creates hash for Custom metric" do
+      metric = Custom.new
+      metric.name = "post_count"
+      metric.description = "Total number of posts"
+      metric.type = "Guage"
+      metric.value = 120
+
+      expect(metric.to_h).to eq(
+        name: "post_count",
+        labels: nil,
+        description: "Total number of posts",
+        type: "Guage",
+        value: 120,
+        _type: "Custom"
+      )
+    end
+  end
+end

GitHub sha: 0170a5af