Undefined local variable or Method - Testing Puppe

I'm quite new to all of this. I am trying to test out a puppet module using Beaker. I keep getting this:

 NoMethodError: undefined method `describe' for 
 #Beaker::TestCase:0x007fd6f95e6460
 /Users/user1/beaker/Puppet/puppet-files/spec/classes/unit_spec.rb:3  
 /Users/user1/.rvm/gems/ruby-2.2.7/gems/beaker-3.24.0/bin/beaker:9  
 /Users/user1/.rvm/gems/ruby-2.2.7/bin/ruby_executable_hooks:15  
 /Users/user1/.rvm/gems/ruby-2.2.7/bin/ruby_executable_hooks:15.
 This is the command that I'm running - "beaker --hosts myhost.yaml --pre-suite spec".

My unit_spec.rb contains this:

  require 'puppetlabs_spec_helper/rake_tasks'

  describe 'application' do
  context 'applied to supported operating system' do
  on_supported_os.each do |os, facts|
  context "#{os}" do
   let(:facts) do
     facts
   end

   context "without any parameters" do
     let(:params) {{ }}

     it { is_expected.to compile.with_all_deps }
     it { is_expected.to contain_class('files') }
     end
    end
   end
  end


    context 'applied to unsupported operating system' do
    describe 'ubuntu-14-x86_64' do
    let(:facts) {{
     :osfamily        => 'Debian',
     :operatingsystem => 'Ubuntu'
      }}

    it { is_expected.to raise_error(Puppet::Error, /Ubuntu not supported/) }
    end
   end
  end

Any help would be much appreciated! Btw, I am using 'puppetlabs_spec_helper/rake_tasks' due to the fact that when I just used 'spec_helper' it gave me an error that it could not "load such file" even though it was there.

Also, I have tried doing

RSpec.Describe

That did not fix the issue either. I get the following error -

 NameError: undefined local variable or method `on_supported_os' for #Class:0x007f92a61d5e58

I realise that this might be an RSpec Puppet issue, as this module was previously tested through puppet RSpec, however now I am trying to test using Beaker and not quite sure how to fully achieve that!

You're mixing up unit- and VM-based testing.

rspec-puppet (and rspec-puppet-facts' on_supported_os) are for catalog-based unit testing. They do not require a VM, and can give you quick feedback on syntax, and logic of your module.
beaker, and the recommended beaker-rspec add-on, provide full end-to-end testing capabilities, using actual VMs, and testing a complete stack deploy (as defined in you tests).

The main entry point for existing modules is usually rake. Take a look at the existing rake tasks in the module using rake -T. In a well-written module it should have tasks for both rspec-puppet (usually called spec), and beaker (often called beaker, or acceptance).

If it is your own module, you also might want to look into the new Puppet Development Kit to get the most important tools in a single installer.