This will not work. The Response constructor expects a string or an object castable to string. ConstraintViolationList is not

hmm, sorry, actually it is. I never used the string casting on it though (and it is there only for debugging purpose anyway, so using print_r in the doc would at least make it clear it is not production-ready)

It has been tested by me and my workmate.

Using print_r returns a big output with a lot of noise. Nothing to do with
the expected results as describe in the doc.

When passing directly $errors, the output is exaclty the one described in
the doc. :)

Edit: Ok. Seen your second message :

I'm not against the usage of print_r, but in this case the description in
the doc should be accurate. Because it says the output should be
"Acme\BlogBundle\Author.name: This value should not be blank" but it's not
that at all. It's a big frightening bunch of data ;)

I didn't know you could do this either :), but makes sense! For clarification, I just split it into multiple lines and added a note at sha:1a425cc. You don't get the nice-ness of relying on the automatic(string) casting inResponse, but this is pretty much just for debugging/playing, so I think clarity is more important.