Improve no Symbol leak tests to be more reliable

test/integration/security_test.rb

@@ -44,8 +44,7 @@ class SecurityTest < Minitest::Test
   end
 
   def test_does_not_permanently_add_filters_to_symbol_table
-    current_symbols = Symbol.all_symbols
+    assert_no_new_symbols do
-
       # MRI imprecisely marks objects found on the C stack, which can result
       # in uninitialized memory being marked. This can even result in the test failing
       # deterministically for a given compilation of ruby. Using a separate thread will
@@ -58,18 +57,26 @@ class SecurityTest < Minitest::Test
       end.join
 
       GC.start
-
+    end
-    assert_equal([], Symbol.all_symbols - current_symbols)
   end
 
   def test_does_not_add_drop_methods_to_symbol_table
-    current_symbols = Symbol.all_symbols
+    assert_no_new_symbols do
-
       assigns = { 'drop' => Drop.new }
       assert_equal("", Template.parse("{{ drop.custom_method_1 }}", assigns).render!)
       assert_equal("", Template.parse("{{ drop.custom_method_2 }}", assigns).render!)
       assert_equal("", Template.parse("{{ drop.custom_method_3 }}", assigns).render!)
+    end
+  end
 
+  def assert_no_new_symbols
+    # Run once to trigger any first-time initialization which might create some symbols,
+    # for example autoload or lazy method parsing might create symbols on first execution.
+    yield
+
+    # Ensure no new symbols for further runs, i.e. the code does not leak symbols
+    current_symbols = Symbol.all_symbols
+    yield
     assert_equal([], Symbol.all_symbols - current_symbols)
   end