proposal: testing: allow regexps to specify example output

[posener]

Please answer these questions before submitting your issue. Thanks!

What version of Go are you using (go version)?

go version go1.7.4 linux/amd64

What operating system and processor architecture are you using (go env)?

GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/eyal/go:/home/eyal/home/go"
GORACE=""
GOROOT="/usr/local/go"
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
CC="gcc"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build162642716=/tmp/go-build -gno-record-gcc-switches"
CXX="g++"
CGO_ENABLED="1"

What did you do?

Wrote a testable example.

What did you expect to see?

A possibility to define Output lines with a regular expression.

What did you see instead?

Only plan text is supported.

[mvdan]

Why do you need this, exactly? Is the plaintext output too big or non-deterministic?

The point of output lines is readability and simplicity, and I think regexes would just add complexity.

[posener]

I have a program that part of the output there is a time duration, that i would like to give an example for.
I think that making a regular expression optional won't harm anything in the simplicity of the example tests.
In the current example system I can't test this program.

[ALTree]

Note that you'll also need to introduce an alternative prefix (not Output:) or you'll break existing tests for people that for example wrote Output: \d expecting a literal match with "\d".

[minux]

you could sanitize the output before printing. (e.g. use regexp to replace the number with a fixed number before print them.) Not only does this not require a new facility, it also allows the users to use older versions of Go.

[posener]

I saw in the code that there is unsorted option for the output, you use it by prefixing the output: unsorted Output:. (it is not documented)
We could do something similar, so it won't break non-regex output.

[rsc]

I think we'd prefer not to further complicate output tests. Doing something like replacing the time with "TIMESTAMP" in the output would be better. Or just don't print it in the first place.

[bradfitz]

I also don't want to do anything here. The whole point of examples to be simple.

Once you need a way to normalize the output, you've already failed at being simple.

[rsc]

Declining for @golang/proposal-review

[gopherbot]

CL https://golang.org/cl/36050 mentions this issue.