What is the meaning of はずでしょう


I was listening to a song and the following lyrics came up:

> 試されていくはずでしょう

Does combining はず+でしょう just strengthen the "must be, probably" idea or is
there some other meaning?

I interpret this as something like "It "must probably" going to be
tested/tried". I know it sounds a bit off, but is it something along these
lines?

[Song](https://youtu.be/2PsK1IuQXhY):

> いくつもの声が  
>  この空を超えて  
>  輝いてまた消えるよ  
>  戸惑いの中で  
>  ただ意味を求め  
>  **試されてゆくはずでしょう**
>
> ひらひらひら ひらひらひら 落ちるように  
>  嬉しいこと 悲しいこと  
>  全て抱いて生きてきた




Basically, `～はずでしょう` can only be natural when it is an interrogative.

Assuming the sentence is a question (though the question mark is missing as
it's lyrics), `試されてゆくはずでしょう？` is meaning "It must be tested in the future,
right?".

If it's a declarative sentence, its meaning is ambiguous since the usage is
unusual. However, it might be interpreted as being equivalent to `試されてゆくはずだ`
(here `でしょう` is considered to be used as a substitute for `だ` to enhance its
lyricism).

