go: testing: bad output formatting when test stdout ends in an incomplete line

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

$ go version
go version go1.14.1 darwin/amd64

Does this issue reproduce with the latest release?

Yes

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

$ go env
GO111MODULE="on"
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/pete/Library/Caches/go-build"
GOENV="/Users/pete/Library/Application Support/go/env"
GOEXE=""
GOFLAGS=" -mod="
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GONOPROXY="github.com/circleci"
GONOSUMDB="github.com/circleci"
GOOS="darwin"
GOPATH="/Users/pete/Source/go"
GOPRIVATE="github.com/circleci"
GOPROXY="direct"
GOROOT="/usr/local/Cellar/go/1.14.1/libexec"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/Cellar/go/1.14.1/libexec/pkg/tool/darwin_amd64"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="<<SOMETHING>>/go.mod"
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/lh/8qc651cn25n1knh824hcyd0r0000gn/T/go-build757047380=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

package testissue

import (
	"fmt"
	"testing"
)

func TestBad(t *testing.T) {
	// No newline below
	fmt.Print("bad output")
}

func TestGood(t *testing.T) {
	// Print a newline below
	fmt.Println("good output")
}

then run:

go test -json ./testissue

What is the issue?

The JSON output seems corrupted for the “bad” test. You can see that it is missing a “pass” action.

The issue appears to be in the conversion the test2json command is doing from stdout of the test runner into JSON. https://github.com/golang/go/blob/master/src/cmd/internal/test2json/test2json.go

{"Time":"2020-03-25T10:07:16.831092Z","Action":"run","Package":"github.com/circleci/distributor/testissue","Test":"TestBad"}
{"Time":"2020-03-25T10:07:16.83137Z","Action":"output","Package":"github.com/circleci/distributor/testissue","Test":"TestBad","Output":"=== RUN   TestBad\n"}
{"Time":"2020-03-25T10:07:16.831384Z","Action":"output","Package":"github.com/circleci/distributor/testissue","Test":"TestBad","Output":"bad output--- PASS: TestBad (0.00s)\n"}
{"Time":"2020-03-25T10:07:16.831401Z","Action":"run","Package":"github.com/circleci/distributor/testissue","Test":"TestGood"}
{"Time":"2020-03-25T10:07:16.831405Z","Action":"output","Package":"github.com/circleci/distributor/testissue","Test":"TestGood","Output":"=== RUN   TestGood\n"}
{"Time":"2020-03-25T10:07:16.831414Z","Action":"output","Package":"github.com/circleci/distributor/testissue","Test":"TestGood","Output":"good output\n"}
{"Time":"2020-03-25T10:07:16.831423Z","Action":"output","Package":"github.com/circleci/distributor/testissue","Test":"TestGood","Output":"--- PASS: TestGood (0.00s)\n"}
{"Time":"2020-03-25T10:07:16.831426Z","Action":"pass","Package":"github.com/circleci/distributor/testissue","Test":"TestGood","Elapsed":0}
{"Time":"2020-03-25T10:07:16.831443Z","Action":"output","Package":"github.com/circleci/distributor/testissue","Output":"PASS\n"}
{"Time":"2020-03-25T10:07:16.831486Z","Action":"output","Package":"github.com/circleci/distributor/testissue","Output":"ok  \tgithub.com/circleci/distributor/testissue\t0.149s\n"}
{"Time":"2020-03-25T10:07:16.833206Z","Action":"pass","Package":"github.com/circleci/distributor/testissue","Elapsed":0.151}