Merge session arg with existing session instead of overwriting

This may break existing tests that are asserting the whole session contents
but should not break existing tests that are asserting individual keys - e.g:

class SomeControllerTest < ActionController::TestCase
  setup do
    session['user_id'] = 1
  end

  test "some test" do
    get :some_action, nil, { 'another_var' => 2 }

    # This assertion will now fail
    assert_equal({ 'another_var' => 2 }, session)

    # This assertion will still pass
    assert_equal 2, session['another_var]
  end
end

Fixes #1529.

1 files changed, 1 insertions, 1 deletions

diff --git a/actionpack/lib/action_controller/test_case.rb b/actionpack/lib/action_controller/test_case.rb
index 66a4808e36..7db7d270e5 100644
--- a/actionpack/lib/action_controller/test_case.rb
+++ b/actionpack/lib/action_controller/test_case.rb
@@ -471,7 +471,7 @@ module ActionController
 
         @request.assign_parameters(@routes, controller_class_name, action.to_s, parameters)
 
-        @request.session = ActionController::TestSession.new(session) if session
+        @request.session.update(session) if session
         @request.session["flash"] = @request.flash.update(flash || {})
         @request.session["flash"].sweep