input: Write a function to retrieve the title of a post given its slug.
  assert get_post_title_by_slug("example-slug") == "Example Title"
  assert get_post_title_by_slug("another-slug") == "Another Title"
  assert get_post_title_by_slug("yet-another-slug") == "Yet Another Title"
output: def get_post_title_by_slug(slug):
      posts = {
          "example-slug": "Example Title",
          "another-slug": "Another Title",
          "yet-another-slug": "Yet Another Title"
      }
      return posts.get(slug, "")