title: Codeception error "Class Yii not found" when trying to run
body: <p>Currently working on a project for my apprenticeship. I have made some automated tests. I initialised codeception by running and built suite using</p>
  
  <pre><code>codecept bootstrap
  codecept build
  </code></pre>
  
  <p>These 2 commands worked as expected but when I try to run the tests I get </p>
  
  <pre><code>FATAL ERROR. TESTS NOT FINISHED.
  Class 'Yii' not found 
  in /srv/http/blog/vendor/codeception/codeception/src/Codeception/Module/Yii2.php:242
  </code></pre>
  
  <p>Any got any ideas? I have looked at both Yii's and Codeceptions documentation but cannot find the solution. </p>
  
  <p><em>UPDATE</em>
  new error message </p>
  
  <pre><code>FATAL ERROR. TESTS NOT FINISHED.
  Class 'Yii' not found 
  in /srv/http/blog/vendor/yiisoft/yii2/helpers/BaseUrl.php:129
  </code></pre>