module TestFunctions
  def abc
    puts 123
  end
end

>> TestFunctions.instance_methods
=> ["abc"]

>> TestFunctions.abc
NoMethodError: undefined method `abc' for TestFunctions:Module from (irb):3

>> TestFunctions::abc
NoMethodError: undefined method `abc' for TestFunctions:Module from (irb):4

defined?(TestFunctions::abc) #=> nil, but
TestFunctions.method_defined? :abc #=> true

module Foo
  def self.method_one
  end

  def Foo.method_two
  end

  class << self
    def method_three
    end
  end
end

module Foo
  def self.method_one
  end

  def Foo.method_two
  end

  class << self
    def method_three
    end
  end

  def method_four
  end

  module_function :method_four
end

module TestFunctions
  def abc
    puts 123
  end

  module_function :abc
end

TestFunctions.abc  # => 123

module Utilities

  def compute_hello(input_string)
     return "Hello #{input_string}"
  end

end

require "test_helper"
require "utilities"

class MyTest < ActiveSupport::TestCase
  include Utilities

  def test_compute_hello
    x = compute_hello(input_string="Miles")
    print x
    assert x=="Hello Miles", "Incorrect Response"
  end

end

>> class MyTest
>>   include TestFunctions
>> end
=> MyTest
>> MyTest.new.abc
123
=> nil

module TestFunctions
  def TestFunctions.abc
    puts 123
  end
end

require 'test_functions'
TestFunctions.abc

module TestFunctions
  def abc
    puts 123
  end
end