Fix another false assertions

Found another false assertions. related to https://github.com/rails/rails/pull/16998

To find false assertions, I used this method and put it into `ActiveSupport::TestCase`:

```ruby
def assert(test, msg = nil)
  if !(msg.nil? || msg.is_a?(Proc)) && !msg.is_a?(String) || msg == test
    raise "false assertion: test: #{test}, msg: #{msg}"
  else
    super
  end
end
```

It mightn't capture all false assertions but it'e better than doing nothing.