Inside "Sample Test" block after declaration of create_chain_for_test method add these two lines:

start = create_chain_for_test(2, 5)
Test.assert_equals(loop_size(start),5)

That is enough to make test run.

You get that error because you can't run tests. The author has configured the tests to show you how the tail and loop are created.

That said i'm confused as heck about what the Node even has. It doesn't seem to have a value available with .value so how we determine loop from tail I have no idea

Using Ruby.

#use this if you want to create your code on you computer the class of the node is in the description

The the Node class is not in the description.

When running "Test", I get an unexpected error:

Response received but no data was written to STDOUT or STDERR.

Even when I tried with a very simple solution that's wrong but should not "break":

def loop_size(node)
  puts "Hello"
  0
end