# File lib/test/unit/assertions.rb, line 550
      def assert_throw(expected_object, message="", &proc)
        _wrap_assertion do
          begin
            catch([]) {}
          rescue TypeError
            assert_instance_of(Symbol, expected_object,
                               "assert_throws expects the symbol that should be thrown for its first argument")
          end
          assert_block("Should have passed a block to assert_throw.") do
            block_given?
          end
          caught = true
          begin
            catch(expected_object) do
              proc.call
              caught = false
            end
            full_message = build_message(message,
                                         "<?> should have been thrown.",
                                         expected_object)
            assert_block(full_message) {caught}
          rescue NameError, ArgumentError, ThreadError => error
            raise unless UncaughtThrow[error.class] =~ error.message
            tag = $1
            tag = tag[1..-1].intern if tag[0, 1] == ":"
            full_message = build_message(message,
                                         "<?> expected to be thrown but\n" +
                                         "<?> was thrown.",
                                         expected_object, tag)
            flunk(full_message)
          end
        end
      end