cmd/go: go test -failfast doesn't stop immediately with t.Parallel()

[timoha]

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

$ go version
go version go1.10.7 linux/amd64

Does this issue reproduce with the latest release?

Yes.

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

go env Output

$ go env
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/jenkins/.cache/go-build"
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/go"
GORACE=""
GOROOT="/usr/local/go"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
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 -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build781955494=/tmp/go-build -gno-record-gcc-switches"

What did you do?

func TestParallel1(t *testing.T) {
    t.Parallel()
    t.FailNow()
}

func TestParallel2(t *testing.T) {
    t.Parallel()
}

run with go test -v -failfast -parallel 1 returns:

=== RUN   TestParallel1
=== PAUSE TestParallel1
=== RUN   TestParallel2
=== PAUSE TestParallel2
=== CONT  TestParallel1
=== CONT  TestParallel2
--- PASS: TestParallel2 (0.00s)
--- FAIL: TestParallel1 (0.00s)
FAIL
exit status 1
FAIL	test	0.075s

What did you expect to see?

TestParallel2 not continue.

What did you see instead?

TestParallel2 continued execution.

[bcmills]

CC @jayconrod

[bcmills]

I doubt we'll get to this in Go 1.13, but I plan to do some work on the testing package for 1.14.