Revert "cmd/go: fail if a test binary exits with no output"

This reverts CL 184457.

Reason for revert: introduced failures in the regression test for #18153.

Fixes #34791
Updates #29062

Change-Id: I4040965163f809083c023be055e69b1149d6214e
Reviewed-on: https://go-review.googlesource.com/c/go/+/200106
Run-TryBot: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Alexander Rakoczy <alex@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/go/internal/test/test.go

@@ -1048,18 +1048,6 @@ func (lockedStdout) Write(b []byte) (int, error) {
 	return os.Stdout.Write(b)
 }
 
-type outputChecker struct {
-	w         io.Writer
-	anyOutput bool
-}
-
-func (o *outputChecker) Write(p []byte) (int, error) {
-	if !o.anyOutput && len(bytes.TrimSpace(p)) > 0 {
-		o.anyOutput = true
-	}
-	return o.w.Write(p)
-}
-
 // builderRunTest is the action for running a test binary.
 func (c *runCache) builderRunTest(b *work.Builder, a *work.Action) error {
 	if a.Failed {
@@ -1079,7 +1067,6 @@ func (c *runCache) builderRunTest(b *work.Builder, a *work.Action) error {
 	}
 
 	var buf bytes.Buffer
-	buffered := false
 	if len(pkgArgs) == 0 || testBench {
 		// Stream test output (no buffering) when no package has
 		// been given on the command line (implicit current directory)
@@ -1106,16 +1093,9 @@ func (c *runCache) builderRunTest(b *work.Builder, a *work.Action) error {
 			stdout = io.MultiWriter(stdout, &buf)
 		} else {
 			stdout = &buf
-			buffered = true
 		}
 	}
 
-	// Keep track of whether we've seen any output at all. This is useful
-	// later, to avoid succeeding if the test binary did nothing or didn't
-	// reach the end of testing.M.Run.
-	outCheck := outputChecker{w: stdout}
-	stdout = &outCheck
-
 	if c.buf == nil {
 		// We did not find a cached result using the link step action ID,
 		// so we ran the link step. Try again now with the link output
@@ -1129,7 +1109,7 @@ func (c *runCache) builderRunTest(b *work.Builder, a *work.Action) error {
 		c.tryCacheWithID(b, a, a.Deps[0].BuildContentID())
 	}
 	if c.buf != nil {
-		if !buffered {
+		if stdout != &buf {
 			stdout.Write(c.buf.Bytes())
 			c.buf.Reset()
 		}
@@ -1227,19 +1207,6 @@ func (c *runCache) builderRunTest(b *work.Builder, a *work.Action) error {
 
 	mergeCoverProfile(cmd.Stdout, a.Objdir+"_cover_.out")
 
-	if err == nil && !testList && !outCheck.anyOutput {
-		// If a test does os.Exit(0) by accident, 'go test' may succeed
-		// and it can take a while for a human to notice the package's
-		// tests didn't actually pass.
-		//
-		// If a test binary ran without error, it should have at least
-		// printed something, such as a PASS line.
-		//
-		// The only exceptions are when no tests have run, and the
-		// -test.list flag, which just prints the names of tests
-		// matching a pattern.
-		err = fmt.Errorf("test binary succeeded but did not print anything")
-	}
 	if err == nil {
 		norun := ""
 		if !testShowPass && !testJSON {
@@ -1260,7 +1227,7 @@ func (c *runCache) builderRunTest(b *work.Builder, a *work.Action) error {
 		fmt.Fprintf(cmd.Stdout, "FAIL\t%s\t%s\n", a.Package.ImportPath, t)
 	}
 
-	if !buffered {
+	if cmd.Stdout != &buf {
 		buf.Reset() // cmd.Stdout was going to os.Stdout already
 	}
 	return nil

src/cmd/go/testdata/script/test_exit.txt

-env GO111MODULE=on
-
-# If a test exits with a zero status code, 'go test' prints its own error
-# message and fails.
-! go test ./zero
-! stdout ^ok
-! stdout 'exit status'
-stdout 'did not print anything'
-stdout ^FAIL
-
-# If a test exits with a non-zero status code, 'go test' fails normally.
-! go test ./one
-! stdout ^ok
-stdout 'exit status'
-! stdout 'did not print anything'
-stdout ^FAIL
-
-# Ensure that other flags still do the right thing.
-go test -list=. ./zero
-stdout ExitZero
-
-! go test -bench=. ./zero
-stdout 'did not print anything'
-
-# 'go test' with no args streams output without buffering. Ensure that it still
-# catches a zero exit with missing output.
-cd zero
-! go test
-stdout 'did not print anything'
-cd ../normal
-go test
-stdout ^ok
-cd ..
-
-# If a TestMain prints something and exits with a zero status code, 'go test'
-# shouldn't complain about that. It's a common way to skip testing a package
-# entirely.
-go test ./main_zero_warning
-! stdout 'skipping all tests'
-stdout ^ok
-
-# With -v, we'll see the warning from TestMain.
-go test -v ./main_zero_warning
-stdout 'skipping all tests'
-stdout ^ok
-
-# Listing all tests won't actually give a result if TestMain exits. That's okay,
-# because this is how TestMain works. If we decide to support -list even when
-# TestMain is used to skip entire packages, we can change this test case.
-go test -list=. ./main_zero_warning
-stdout 'skipping all tests'
-! stdout TestNotListed
-
-# If a TestMain prints nothing and exits with a zero status code, 'go test'
-# should fail.
-! go test ./main_zero_nowarning
-stdout 'did not print anything'
-
-# A test that simply prints "PASS" and exits with a zero status code shouldn't
-# be OK, but we don't catch that at the moment. It's hard to tell if any test
-# started but didn't finish without using -test.v.
-go test ./fake_pass
-stdout ^ok
-
--- go.mod --
-module m
-
--- ./normal/normal.go --
-package normal
--- ./normal/normal_test.go --
-package normal
-
-import "testing"
-
-func TestExitZero(t *testing.T) {
-}
-
--- ./zero/zero.go --
-package zero
--- ./zero/zero_test.go --
-package zero
-
-import (
-	"os"
-	"testing"
-)
-
-func TestExitZero(t *testing.T) {
-	os.Exit(0)
-}
-
--- ./one/one.go --
-package one
--- ./one/one_test.go --
-package one
-
-import (
-	"os"
-	"testing"
-)
-
-func TestExitOne(t *testing.T) {
-	os.Exit(1)
-}
-
--- ./main_zero_warning/zero.go --
-package zero
--- ./main_zero_warning/zero_test.go --
-package zero
-
-import (
-	"fmt"
-	"os"
-	"testing"
-)
-
-func TestMain(m *testing.M) {
-	fmt.Println("skipping all tests")
-	os.Exit(0)
-}
-
-func TestNotListed(t *testing.T) {}
-
--- ./main_zero_nowarning/zero.go --
-package zero
--- ./main_zero_nowarning/zero_test.go --
-package zero
-
-import (
-	"os"
-	"testing"
-)
-
-func TestMain(m *testing.M) {
-	os.Exit(0)
-}
-
--- ./fake_pass/fake.go --
-package fake
--- ./fake_pass/fake_test.go --
-package fake
-
-import (
-	"fmt"
-	"os"
-	"testing"
-)
-
-func TestFakePass(t *testing.T) {
-	fmt.Println("PASS")
-	os.Exit(0)
-}

src/cmd/internal/goobj/goobj_test.go

@@ -29,7 +29,9 @@ var (
 )
 
 func TestMain(m *testing.M) {
-	testenv.MainMust(testenv.HasGoBuild)
+	if !testenv.HasGoBuild() {
+		return
+	}
 
 	if err := buildGoobj(); err != nil {
 		fmt.Println(err)

src/cmd/nm/nm_test.go

@@ -26,7 +26,9 @@ func TestMain(m *testing.M) {
 }
 
 func testMain(m *testing.M) int {
-	testenv.MainMust(testenv.HasGoBuild)
+	if !testenv.HasGoBuild() {
+		return 0
+	}
 
 	tmpDir, err := ioutil.TempDir("", "TestNM")
 	if err != nil {

src/cmd/objdump/objdump_test.go

@@ -22,7 +22,9 @@ import (
 var tmp, exe string // populated by buildObjdump
 
 func TestMain(m *testing.M) {
-	testenv.MainMust(testenv.HasGoBuild)
+	if !testenv.HasGoBuild() {
+		return
+	}
 
 	var exitcode int
 	if err := buildObjdump(); err == nil {

src/go/build/deps_test.go

@@ -202,7 +202,7 @@ var pkgDeps = map[string][]string{
 	"testing":               {"L2", "flag", "fmt", "internal/race", "os", "runtime/debug", "runtime/pprof", "runtime/trace", "time"},
 	"testing/iotest":        {"L2", "log"},
 	"testing/quick":         {"L2", "flag", "fmt", "reflect", "time"},
-	"internal/testenv":      {"L2", "OS", "flag", "fmt", "testing", "syscall", "internal/cfg"},
+	"internal/testenv":      {"L2", "OS", "flag", "testing", "syscall", "internal/cfg"},
 	"internal/lazyregexp":   {"L2", "OS", "regexp"},
 	"internal/lazytemplate": {"L2", "OS", "text/template"},
 

src/internal/testenv/testenv.go

@@ -13,7 +13,6 @@ package testenv
 import (
 	"errors"
 	"flag"
-	"fmt"
 	"internal/cfg"
 	"os"
 	"os/exec"
@@ -33,14 +32,6 @@ func Builder() string {
 	return os.Getenv("GO_BUILDER_NAME")
 }
 
-func MainMust(cond func() bool) {
-	if !cond() {
-		fmt.Println("testenv: warning: can't run any tests")
-		fmt.Println("SKIP")
-		os.Exit(0)
-	}
-}
-
 // HasGoBuild reports whether the current system can build programs with ``go build''
 // and then run them with os.StartProcess or exec.Command.
 func HasGoBuild() bool {