Improve middleware spec with Rack::Lint and cleanup

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: dpep

spec/singed/middleware_spec.rb

@@ -1,39 +1,48 @@
+# frozen_string_literal: true
+
+require "tmpdir"
+
 describe Singed::RackMiddleware do
   subject do
     instance.call(env)
   end
 
-  let(:app) { ->(*) { [200, {'Content-Type' => 'text/plain'}, ['OK']] } }
+  let(:app) { ->(*) { [200, {"content-type" => "text/plain"}, ["OK"]] } }
   let(:instance) { described_class.new(app) }
-  let(:env) { Rack::MockRequest.env_for('/', headers) }
+  let(:env) { Rack::MockRequest.env_for("/", headers) }
   let(:headers) { {} }
 
-  it 'returns a proper rack response' do
-    status, _ = subject
-    expect(status).to eq 200
+  before do
+    allow_any_instance_of(Singed::Flamegraph).to receive(:open)
+    Singed.output_directory = Dir.mktmpdir("singed-spec")
+  end
+
+  it "returns a proper rack response" do
+    linted_app = Rack::Lint.new(instance)
+    expect { linted_app.call(env) }.not_to raise_error
   end
 
-  it 'does not capture a flamegraph by default' do
+  it "does not capture a flamegraph by default" do
     expect(instance).not_to receive(:flamegraph)
     subject
   end
 
-  context 'when enabled' do
+  context "when enabled" do
     before { allow(instance).to receive(:capture_flamegraph?).and_return(true) }
 
-    it 'captures a flamegraph' do
-      expect(instance).to receive(:flamegraph)
+    it "captures a flamegraph" do
+      expect(instance).to receive(:flamegraph).and_call_original
       subject
     end
   end
 
-  describe '.capture_flamegraph?' do
+  describe ".capture_flamegraph?" do
     subject { instance.capture_flamegraph?(env) }
 
     it { is_expected.to be false }
 
-    context 'when HTTP_X_SINGED is true' do
-      let(:headers) { { 'HTTP_X_SINGED' => 'true' } }
+    context "when HTTP_X_SINGED is true" do
+      let(:headers) { {"HTTP_X_SINGED" => "true"} }
 
       it { is_expected.to be true }
     end