testing: stdout output with no newline produces confusing/corrupt -v output

[neild]

package out_test

import (
	"fmt"
	"testing"
)

func TestOut(t *testing.T) { fmt.Print("TestOut") }

$ go test .
ok  	testout	0.016s
$ go test . -v
=== RUN   TestOut
Test--- PASS: TestOut (0.00s)
PASS
ok  	testout	0.017s

Output to stdout during tests is captured and printed along with t.Logf et al. output when -v is supplied. If the output doesn't end with a newline, the output is as above.

We have some tools that parse test output which get confused in this situation. It's easy enough to avoid (just print a newline in your test) but it would also be pretty trivial for the testing package could add a newline when one is missing.

[mvdan]

This does seem like something to fix, but note that you should be running go test -json to parse the test results.

[agnivade]

There are some tools like https://github.com/rakyll/gotest which parses command line go test output. This will break those I believe.

[mvdan]

The plaintext output has already been changed in the past, for example in 3a8b9cf. And now that there is go test -json, I'd imagine that it's less of a problem to make small changes to the plaintext output.

[neild]

I don't think we should change anything other than, possibly, adding a newline at the end of the test output when one isn't present. I'd be surprised if anything depends on the current behavior. e.g., https://github.com/rakyll/gotest will fail to parse test output that doesn't end in a newline.

I actually didn't know about go test -json! That's definitely a better approach for automated parsing. I lean towards saying we should add that missing newline in the text output anyway when needed; I can't imagine anyone actually wants to see the output in the example above.

[neild]

Heh. So it turns out go test -json works by parsing the normal text output...and it gets just as confused by this case.

{"Time":"2018-07-11T09:30:22.855058114-07:00","Action":"run","Package":"_/tmp/testout","Test":"TestOut"}
{"Time":"2018-07-11T09:30:22.855222613-07:00","Action":"output","Package":"_/tmp/testout","Test":"TestOut","Output":"=== RUN   TestOut\n"}
{"Time":"2018-07-11T09:30:22.855255176-07:00","Action":"output","Package":"_/tmp/testout","Test":"TestOut","Output":"Out--- PASS: TestOut (0.00s)\n"}
{"Time":"2018-07-11T09:30:22.855268402-07:00","Action":"output","Package":"_/tmp/testout","Output":"PASS\n"}
{"Time":"2018-07-11T09:30:22.855331884-07:00","Action":"output","Package":"_/tmp/testout","Output":"ok  \t_/tmp/testout\t0.011s\n"}
{"Time":"2018-07-11T09:30:22.856056764-07:00","Action":"pass","Package":"_/tmp/testout","Elapsed":0.012}

Contrast to the same test with a newline in the output, which correctly includes a "pass" action for the TestOut test:

{"Time":"2018-07-11T09:30:54.037472791-07:00","Action":"run","Package":"_/tmp/testout","Test":"TestOut"}
{"Time":"2018-07-11T09:30:54.037651722-07:00","Action":"output","Package":"_/tmp/testout","Test":"TestOut","Output":"=== RUN   TestOut\n"}
{"Time":"2018-07-11T09:30:54.037666684-07:00","Action":"output","Package":"_/tmp/testout","Test":"TestOut","Output":"Out\n"}
{"Time":"2018-07-11T09:30:54.037685506-07:00","Action":"output","Package":"_/tmp/testout","Test":"TestOut","Output":"--- PASS: TestOut (0.00s)\n"}
{"Time":"2018-07-11T09:30:54.037695155-07:00","Action":"pass","Package":"_/tmp/testout","Test":"TestOut","Elapsed":0}
{"Time":"2018-07-11T09:30:54.037708614-07:00","Action":"output","Package":"_/tmp/testout","Output":"PASS\n"}
{"Time":"2018-07-11T09:30:54.037761824-07:00","Action":"output","Package":"_/tmp/testout","Output":"ok  \t_/tmp/testout\t0.011s\n"}
{"Time":"2018-07-11T09:30:54.038279369-07:00","Action":"pass","Package":"_/tmp/testout","Elapsed":0.011}