formatter: remove empty message string in assert.Equalf conversions (autofix)

[ghouscht]

Hey,
While working on enabling testifylint, specifically the formatter (etcd-io/etcd#18741) we found a potential improvement for the automatic fix in the formatter check with require-f-funcs option enabled.

In the codebase we found several occasions of assertions like this:

assert.Equal(t, want, got, "")

testifylint autofix automatically replaced them with that: (assert.Equalf)

assert.Equalf(t, want, got, "")

which is fine but I belive it would be better to remove the empty message string and replace as follows:

assert.Equal(t, want, got)

What do you think about that? Would you accept a PR that changes this behaviour?

[Antonboom]

@ghouscht hi!

thank you for issue

these are really strange occasions :D

What do you think about that?

I am ok this that.

Would you accept a PR that changes this behaviour?

Yes, appreciated.

But need to introduce new messages for this

formatter: empty format string
formatter: empty string among formatted arguments

And to test it carefully:

1. assert.Equal(t, want, got, "") -> assert.Equal(t, want, got)
2. assert.Equalf(t, want, got, "") -> assert.Equal(t, want, got)
3. assert.Equal(t, want, got, "msg %d", "") -> no autofix, warn on empty string in args
4. assert.Equal(t, want, got, "msg", "") -> no autofix, warn on empty string in args
5. assert.Equal(t, want, got, "msg %d %v", "", "3") -> no autofix, warn on empty string in args
6. maybe some Sprintf cases? please, look at current formatter tests and grep some ideas

but 3-5 looks like issue in go vet's printf, that could be natively inherited by testifylint without extra dev on our side.