wrong number arguments (0 for 1) (ArgumentError)

Looks like rspec is not passing any arguments to the method, even though they're written in the spec file.

The method:

def echo(msg)
  msg
end

The test:

require './echo.rb'

describe echo do
  it 'echoes' do
    expect(echo('hello')).to eq('hello')
  end
end

terminal output:

/home/.../scratch/echo.rb:1:in `echo': wrong number of arguments (0 for 1) (ArgumentError)
from /home/.../scratch/scratch_spec.rb:3:in '<top (required)>'
from /home/.../.rvm/gems/ruby-2.2.1/gems/rspec-core-3.4.1/lib/rspec/core/configuration.rb:1361:in 'load'
...