Introduce #with_formats_and_variants to prevent problems with mutating finder object

2 files changed, 21 insertions, 0 deletions

diff --git a/actionview/test/template/digestor_test.rb b/actionview/test/template/digestor_test.rb
index 1c47952f54..72d1f43f12 100644
--- a/actionview/test/template/digestor_test.rb
+++ b/actionview/test/template/digestor_test.rb
@@ -40,6 +40,14 @@ class FixtureFinder
   def disable_cache(&block)
     yield
   end
+
+  def with_formats_and_variants(new_formats, new_variants)
+    old_formats, old_variants = formats, variants
+    self.formats, self.variants = new_formats, new_variants
+    yield
+  ensure
+    self.formats, self.variants = old_formats, old_variants
+  end
 end
 
 class TemplateDigestorTest < ActionView::TestCase
diff --git a/actionview/test/template/lookup_context_test.rb b/actionview/test/template/lookup_context_test.rb
index 4f7823045e..b11f252110 100644
--- a/actionview/test/template/lookup_context_test.rb
+++ b/actionview/test/template/lookup_context_test.rb
@@ -205,6 +205,19 @@ class LookupContextTest < ActiveSupport::TestCase
     @lookup_context.prefixes = ["foo"]
     assert_equal ["foo"], @lookup_context.prefixes
   end
+
+  test "with_formats_and_variants preserves original values after execution" do
+    @lookup_context.formats = [:html]
+    @lookup_context.variants = [:phone]
+
+    @lookup_context.with_formats_and_variants([:xml], [:tablet]) do
+      assert_equal [:xml], @lookup_context.formats
+      assert_equal [:tablet], @lookup_context.variants
+    end
+
+    assert_equal [:html], @lookup_context.formats
+    assert_equal [:phone], @lookup_context.variants
+  end
 end
 
 class LookupContextWithFalseCaching < ActiveSupport::TestCase