title: ScalaTest: Checking that list does not contain element
body: <p>so i am new to scala and i need to check that a List does not contain an element.</p>
  
  <p>here is the code i'm trying to write but abviously my syntax is wrong and i don't know how to do it:</p>
  
  <pre><code>  it should "return unique slugs for all category" in {
      val allCategories = categoryService.getAllCategories("rocket")
      val checkedCategories = List()
      allCategories.foreach(
        category =&gt; checkedCategories should notContains category.slug
      )
    } 
  </code></pre>