Diff command outputs against text file

Instead of diffing two text files against each other, I am attempting to diff the output of a command against a text file. The following excerpt from a robot file does not seem to work:

Diff Files <(cat foo.txt) bar.txt

The output of this robot file excerpt is:

test | FAIL |
<(cat foo.txt) doesn't exist

Should this usage work out of the box, or is it necessary to add this functionality?

Thank you!