stdout messes up go test --json

[tehsphinx]

Note: Possibly related to #33419.

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

$ go version
go version go1.13.6 darwin/amd64

Does this issue reproduce with the latest release?

I'm using the latest release.

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

go env Output

$ go env
GO111MODULE="on"
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/user/Library/Caches/go-build"
GOENV="/Users/user/Library/Application Support/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GONOPROXY="git.rrdc.de"
GONOSUMDB="git.rrdc.de"
GOOS="darwin"
GOPATH="/Users/user/go"
GOPRIVATE="git.rrdc.de"
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/darwin_amd64"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/dev/null"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/40/qhkn9k653kd0rjgtp0mljpb40000gn/T/go-build357004700=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

Running a test that outputs something to stdout without a newline at the end will mess up go test --json.

For example:

package main

import (
	"fmt"
	"testing"
)

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

What did you expect to see?

go test --json should output:

{"Time":"2020-01-15T18:44:23.197981+01:00","Action":"run","Package":"git.raceresult.com/la/TestMain","Test":"TestX"}
{"Time":"2020-01-15T18:44:23.199111+01:00","Action":"output","Package":"git.raceresult.com/la/TestMain","Test":"TestX","Output":"=== RUN   TestX\n"}
{"Time":"2020-01-15T18:44:23.199129+01:00","Action":"output","Package":"git.raceresult.com/la/TestMain","Test":"TestX","Output":"foo"}
{"Time":"2020-01-15T18:44:23.199158+01:00","Action":"output","Package":"git.raceresult.com/la/TestMain","Test":"TestX","Output":"--- PASS: TestX (0.00s)\n"}
{"Time":"2020-01-15T18:44:23.199163+01:00","Action":"pass","Package":"git.raceresult.com/la/TestMain","Test":"TestX","Elapsed":0}
{"Time":"2020-01-15T18:44:23.199229+01:00","Action":"output","Package":"git.raceresult.com/la/TestMain","Output":"PASS\n"}
{"Time":"2020-01-15T18:44:23.199261+01:00","Action":"output","Package":"git.raceresult.com/la/TestMain","Output":"ok  \tgit.raceresult.com/la/TestMain\t0.321s\n"}
{"Time":"2020-01-15T18:44:23.200981+01:00","Action":"pass","Package":"git.raceresult.com/la/TestMain","Elapsed":0.323}

What did you see instead?

go test --json outputs:

{"Time":"2020-01-15T18:36:09.586716+01:00","Action":"run","Package":"git.raceresult.com/la/TestMain","Test":"TestX"}
{"Time":"2020-01-15T18:36:09.586898+01:00","Action":"output","Package":"git.raceresult.com/la/TestMain","Test":"TestX","Output":"=== RUN   TestX\n"}
{"Time":"2020-01-15T18:36:09.586909+01:00","Action":"output","Package":"git.raceresult.com/la/TestMain","Test":"TestX","Output":"foo--- PASS: TestX (0.00s)\n"}
{"Time":"2020-01-15T18:36:09.586914+01:00","Action":"output","Package":"git.raceresult.com/la/TestMain","Output":"PASS\n"}
{"Time":"2020-01-15T18:36:09.586918+01:00","Action":"output","Package":"git.raceresult.com/la/TestMain","Output":"ok  \tgit.raceresult.com/la/TestMain\t(cached)\n"}
{"Time":"2020-01-15T18:36:09.586923+01:00","Action":"pass","Package":"git.raceresult.com/la/TestMain","Elapsed":0}

[ianlancetaylor]

This is the same problem as #33419. Closing as a dup.