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 <[email protected]>
Reviewed-by: Alexander Rakoczy <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>

Author: Bryan C. Mills

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

@@ -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/internal/goobj/goobj_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/nm/nm_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/cmd/objdump/objdump_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/go/build/deps_test.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 {