Regex help required (include with exclude criteria)

Hi all,

We are trying to create an expression that matches, if the sequence is containing the string "test123".
However it should not match, if the sequence also contains the string "nowEXCLUDE".

Example sequences:
1. "abc def ghi jkl mno" --> should not match
2. "abc def ghi test123 jkl mno" --> should match
3. "abc def ghi test123 jkl nowEXCLUDE mno" --> should not match
4. "abc def ghi jkl nowEXCLUDE mno" --> should not match*

We are using the library CATLRegExp and tried a lot on https://regex101.com/ but are not successful.

Any help is greatly appreciated. Thank you.