Issue #3183472 by paulocs Replace drupalPostForm() with drupalGet() and submitForm().

    foreach ($this->variables as $key => $variables) {

      $edit = (array) $variables;

      $this->drupalPostForm('/admin/config/system/google-tag/add', $edit, 'Save');

      $this->drupalGet('/admin/config/system/google-tag/add');

      $this->submitForm($edit, 'Save');

      $text = 'Created @count snippet files for %container container based on configuration.';

      $args = ['@count' => 3, '%container' => $variables->label];