Fix compatibility with --frozen-string-literal

Author: chaadow

.github/workflows/ci.yml

@@ -8,19 +8,23 @@ jobs:
       matrix:
         ruby: [ '3.1', '3.2', '3.3', 'head' ]
         rails: [ '7.1', 'edge' ]
+        rubyopt: [""]
         include:
           - ruby: '2.7'
             rails: '6.1'
           - ruby: '3.0'
             rails: '6.1'
           - ruby: '3.1'
             rails: '7.0'
+          - ruby: '3.3'
+            rails: 'edge'
+            rubyopt: "--enable-frozen-string-literal"
 
     env:
       RAILS_VERSION: ${{ matrix.rails }}
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
 
       - name: Set up Ruby
         uses: ruby/setup-ruby@v1
@@ -29,10 +33,10 @@ jobs:
           bundler-cache: true
 
       - name: Run unit tests
-        run: bundle exec rake test:unit
+        run: bundle exec rake test:unit RUBYOPT="${{ matrix.rubyopt }}"
         timeout-minutes: 3
 
       - name: Run acceptance tests
-        run: bundle exec rake test:acceptance
+        run: bundle exec rake test:acceptance RUBYOPT="${{ matrix.rubyopt }}"
         timeout-minutes: 10
         if: ${{ matrix.rails != 'edge' && matrix.ruby != 'head' }} # Acceptance tests use `gem install rails && rails new`

test/support/application.rb

@@ -168,7 +168,7 @@ def read_streams
       end
 
       def read_stream(stream)
-        output = ""
+        output = +""
         while IO.select([stream], [], [], 0.5) && !stream.eof?
           output << stream.readpartial(10240)
         end