Behat: Support taxonomy term entity references when creating new nodes during testing. Edit vender/drupal/drupalextension/src/Drupal/Driver/Core/Drupal7.php in function exandEntityFields().

Drupal7.php

                // Special handling for entity references.
                elseif ('entityreference' === $info['module']) {
                  $values = explode(',', $value);
                  
                  // Handle taxonomy terms.
                  // @todo generalize.
                  if ($info['settings']['target_type'] == 'taxonomy_term') {                    
                    $i = 0;
                    foreach ($values as $tid) {
                      $new_entity->{$param}[LANGUAGE_NONE][$i]['target_id'] = $tid;
                      $i++;
                    }
                  }
                }