Test Writing: Double Up Null

Created By: Chris Taylor

/ Version: 2023.6.0

Write a method, doubleUp, that accepts a List<String>? and returns a List<String>? where each String in the original list is concatenated with itself. If a String in the list is null, simply pass it through, as shown below. If the passed List is null, return null. Your solution must not use loops and must use at least one lambda expression.

• ["a", "b"] -> ["aa", "bb"]
• ["", null] -> ["", null]
• null -> null

Test Design Challenge

You're challenge is to write tests for this problem described above.

• Provide a method named test that accepts no arguments and does not return a value.
• If the implementation of the class described above is incorrect, your test method should throw an exception.
• If it is correct, do not throw an exception.
• You may want to use Kotlin's assert or check methods