Refactor the test for SafeString.

test/link_shortener/generators/safe_string_test.exs

@@ -7,11 +7,10 @@ defmodule LinkShortener.Generators.SafeStringTest do
 
   test "generate/1 returns random safe string with same length" do
     for expected_length <- @lengths do
-      length = expected_length
+      assert ^expected_length =
+               expected_length
                |> SafeString.generate()
                |> String.length()
-      
-      assert length = expected_length
     end
   end
 end