Add an additional test, improve the error check to fix the tests

Author: tmeire

lib/importmap/npm.rb

@@ -80,7 +80,7 @@ def get_json(uri)
         http.request(request)
       }
 
-      unless response.kind_of? Net::HTTPSuccess
+      unless response.code.to_i < 300
         raise HTTPError, "Unexpected error response #{response.code}: #{response.body}"
       end
 
@@ -115,7 +115,7 @@ def get_audit
       return {} if body.empty?
 
       response = post_json(uri, body)
-      unless response.kind_of? Net::HTTPSuccess
+      unless response.code.to_i < 300
         raise HTTPError, "Unexpected error response #{response.code}: #{response.body}"
       end
       JSON.parse(response.body)

test/npm_test.rb

@@ -67,6 +67,22 @@ class Importmap::NpmTest < ActiveSupport::TestCase
     end
   end
 
+  test "failed vulnerable packages with mock" do
+    response = Class.new do
+      def body
+        { "message" => "Service unavailable" }.to_json
+      end
+
+      def code() "500" end
+    end.new
+
+    @npm.stub(:post_json, response) do
+      assert_raises(Importmap::Npm::HTTPError) do
+        vulnerable_packages = @npm.vulnerable_packages
+      end
+    end
+  end
+
   test "successful vulnerable packages with mock" do
     response = Class.new do
       def body