Add test for GitHub::search_code.

Library/Homebrew/test/utils/github_spec.rb

@@ -0,0 +1,13 @@
+require "utils/github"
+
+describe GitHub do
+  describe "::search_code", :needs_network do
+    it "searches code" do
+      results = subject.search_code("repo:Homebrew/brew", "path:/", "filename:readme", "language:markdown")
+
+      expect(results.count).to eq(1)
+      expect(results.first["name"]).to eq("README.md")
+      expect(results.first["path"]).to eq("README.md")
+    end
+  end
+end