Find and Replace using Regex - change $1 Result to uppercase?

// test

// another test

...

By @RigidCollision

Youps, sorry, when I saw my answer displayed, I understood that, in your question,  the lines starting with / corresponded to your search fields, so, your initial query and your replacement expression are quite correct.

They should work, if not, DW acts as expected, switch to Notepad++.
Sorry again for the noise.

Indeed, the 

\U$1

instruction does not work in DW but as expected in Notepad++.

However (unless you want it to), the initial request you make includes the invisible characters before any first letter, which results in the removal of that character when replacing.

In addition, this query also includes characters that are already capitalized, which is not necessary in itself.

So, I would suggest replacing your query with

(\b[a-z](?!\s))

And

\U$1

 If I find an alternative in DW, I will come back to this post, but often, I make the REGEX in Notepad++, even in Vim

I don't follow.  Can you be more specific?  Give us some examples of the target string you're searching for and what should replace it.