It does, so that’s why this will fail to find a match for Test because it’s looking for an uppercase T and there won’t be any.
{{ trigger.calendar_event.summary | slugify == 'Test' }}
In addition, slugify replaces all spaces and non-ASCII characters with an underscore.
If you removed slugify, it would only find a match if the summary contains the single word Test and nothing else. The == operator requires a perfect match (i.e. it doesn’t check if the summary contains Test among other things, it must only contain the word Test).
I suggest doing it like this:
{{ trigger.calendar_event.summary is search 'Test|cat|Dog|hat' }}
To experiment with it, copy-paste the following into Developer Tools → Template.
{{ 'The dog ate the hat.' is search 'dog|hat|rat|cat' }}