Somewhere on this Wiki I've seen a reference to the "Phrase critiques using 'and' instead of 'but'" form.

I've also seen this from other sources.   However, it has me almost entirely perplexed.  I often find myself coming across as too critical when I use "but".  I.e.: "This code is great, but you didn't write any tests."

All I've been able to come up with is "and if it only" phrasings.  That is, changing "This code is great, but you didn't write any tests." to "This code is great.  And if it only had tests, it would be perfect."

Is this the kind of thing meant by the ReplaceButWithAnd phrase?

''Yes.  And the example above can be improved by saying "This code is great, and when you add tests it will be finished and you can move on to something else."  It's best to make a statement assuming a successful mutually beneficial outcome (or at least assuming a good effort from the person you are addressing).''