instance method _expression_to_callable

# File activesupport/lib/active_support/testing/assertions.rb, line 369
        def _expression_to_callable(callable_or_ruby_source, binding)
          return callable_or_ruby_source if callable_or_ruby_source.respond_to?(:call)

          case callable_or_ruby_source
          when String, Symbol
            -> { eval(callable_or_ruby_source.to_s, binding) }
          else
            raise ArgumentError, "The expression must be a callable object like a Proc, or a String of Ruby code. Got #{callable_or_ruby_source.inspect}"
          end
        end