I know, but he's actually using it in his code. That's why it fails, and there is also another problem:

Finish the solution so that it returns the sum of all the multiples of 3 or 5 BELOW the number passed in.

Maybe this confuses him:

function test(n, expected) {
  let actual = solution(n) // your function, only one argument
  Test.assertEquals(actual, expected, `Expected ${expected}, got ${actual}`)
}

Test.describe("basic tests", function(){
  test(10,23) // 10 here is the number passed to your function, and 23 is the expected value, it depends on the number passed to your function.
})

@Chrono79 JS doesn't care. :)

@plav2019 solveProblem doesn't exist.

Also, you're overcomplicating things. It's not really that complex. :]

Why are you using a second argument in your function? Your function is always called with a single argument in the tests.

Without seeing your code we can only guess. If you post your code, use markdown formatting and mark your post as having spoiler content.

You're probably printing the result instead of returning it.