title: Not able to call method in a gem
body: <br>
  <p>This might be an easy question but I was unfortunately not able to find the answer on Google.</p>
  <p><strong>Context:</strong><br>
  I am working on a project of my own, and I am externalizing some code in a gem (FrenchTaxSystem). It is the first I create a gem and I have difficulties using it properly.</p>
  <p><strong>Problem:</strong><br>
  When calling a method (like testit) defined in the main file (french_tax_system.rb) of my gem I get a &quot;NoMethodError: undefined method `testit' for FrenchTaxSystem:Module&quot;, though I can call constants from this same file  (like FISCAL_NB_PARTS_FOR_MARRIED_COUPLE) and it puzzles me.</p>
  <p>E.g in IRB I get that when calling a method:
  [<img src="https://i.stack.imgur.com/dZ1s4.png" alt="irb error1" />
  And it is the same in my Rspecs tests inside my gem
  <a href="https://i.stack.imgur.com/v44nN.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/v44nN.png" alt="rspec error" /></a></p>
  <p>However when calling a constant I have no error:
  <a href="https://i.stack.imgur.com/Idofm.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Idofm.png" alt="irb working for constants" /></a></p>
  <p><strong>Main file in my gem:</strong><br>
  french_tax_system.rb<br></p>
  <pre><code>module FrenchTaxSystem
    class Error &lt; StandardError; end
  
    # Constants
    ...
    FISCAL_NB_PARTS_FOR_MARRIED_COUPLE = 2
    ...
  
    # Methods
    ## Main method
    def testit
      &quot;test me&quot;
    end
  end
  </code></pre>
  <p><strong>Gem file structure:</strong><br>
  <a href="https://i.stack.imgur.com/Fd8fz.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Fd8fz.png" alt="gem file structure" /></a></p>
  <br>
  <br>
  Thank you in advance for your help,<br>
  Mth0158