ktesting: stop using testing.T when test completes

When testing.T.Log gets called after the test has completed, it panics. There's
also a data race (kubernetes/kubernetes#110854).

Normally that should never happen because tests should ensure that all
goroutines have stopped before returning. But sometimes it is not possible to
do that. ktesting now automatically protects against that by registering a
cleanup function and redirecting all future output into klog.

ktesting/testinglogger.go

@@ -49,6 +49,7 @@ import (
 
 	"github.com/go-logr/logr"
 
+	"k8s.io/klog/v2"
 	"k8s.io/klog/v2/internal/serialize"
 	"k8s.io/klog/v2/internal/verbosity"
 )
@@ -76,22 +77,40 @@ type NopTL struct{}
 func (n NopTL) Helper()                 {}
 func (n NopTL) Log(args ...interface{}) {}
 
-var _TL = NopTL{}
+var _ TL = NopTL{}
 
 // NewLogger constructs a new logger for the given test interface.
 //
+// Beware that testing.T does not support logging after the test that
+// it was created for has completed. If a test leaks goroutines
+// and those goroutines log something after test completion,
+// that output will be printed via the global klog logger with
+// `<test name> leaked goroutine` as prefix.
+//
 // Experimental
 //
 // Notice: This type is EXPERIMENTAL and may be changed or removed in a
 // later release.
 func NewLogger(t TL, c *Config) logr.Logger {
-	return logr.New(&tlogger{
-		t:      t,
-		prefix: "",
-		values: nil,
-		config: c,
-		buffer: new(buffer),
-	})
+	l := tlogger{
+		shared: &tloggerShared{
+			t:      t,
+			config: c,
+		},
+	}
+
+	type testCleanup interface {
+		Cleanup(func())
+		Name() string
+	}
+
+	// Stopping the logging is optional and only done (and required)
+	// for testing.T/B/F.
+	if tb, ok := t.(testCleanup); ok {
+		tb.Cleanup(l.shared.stop)
+		l.shared.testName = tb.Name()
+	}
+	return logr.New(l)
 }
 
 // Buffer stores log entries as formatted text and structured data.
@@ -203,6 +222,7 @@ const (
 // later release.
 type Underlier interface {
 	// GetUnderlying returns the testing instance that logging goes to.
+	// It returns nil when the test has completed already.
 	GetUnderlying() TL
 
 	// GetBuffer grants access to the in-memory copy of the log entries.
@@ -227,35 +247,85 @@ func (b *buffer) Data() Log {
 	return b.log.DeepCopy()
 }
 
+// tloggerShared holds values that are the same for all instances.
+type tloggerShared struct {
+	// mutex protects access to t.
+	mutex sync.Mutex
+
+	// t gets cleared when the test is completed.
+	t TL
+
+	testName  string
+	config    *Config
+	buffer    buffer
+	callDepth int
+}
+
+func (ls *tloggerShared) stop() {
+	ls.mutex.Lock()
+	defer ls.mutex.Unlock()
+	ls.t = nil
+}
+
+// tlogger is the actual LogSink implementation.
 type tlogger struct {
-	t      TL
+	shared *tloggerShared
 	prefix string
 	values []interface{}
-	config *Config
-	buffer *buffer
 }
 
-func (l *tlogger) Init(info logr.RuntimeInfo) {
+func (l tlogger) fallbackLogger() logr.Logger {
+	logger := klog.Background().WithValues(l.values...).WithName(l.shared.testName + " leaked goroutine")
+	if l.prefix != "" {
+		logger = logger.WithName(l.prefix)
+	}
+	// Skip direct caller (= Error or Info) plus the logr wrapper.
+	logger = logger.WithCallDepth(l.shared.callDepth + 1)
+	return logger
+}
+
+func (l tlogger) Init(info logr.RuntimeInfo) {
+	l.shared.callDepth = info.CallDepth
 }
 
-func (l *tlogger) GetCallStackHelper() func() {
-	return l.t.Helper
+func (l tlogger) GetCallStackHelper() func() {
+	l.shared.mutex.Lock()
+	defer l.shared.mutex.Unlock()
+	if l.shared.t == nil {
+		return func() {}
+	}
+
+	return l.shared.t.Helper
 }
 
-func (l *tlogger) Info(level int, msg string, kvList ...interface{}) {
-	l.t.Helper()
+func (l tlogger) Info(level int, msg string, kvList ...interface{}) {
+	l.shared.mutex.Lock()
+	defer l.shared.mutex.Unlock()
+	if l.shared.t == nil {
+		l.fallbackLogger().V(level).Info(msg, kvList...)
+		return
+	}
+
+	l.shared.t.Helper()
 	buffer := &bytes.Buffer{}
 	merged := serialize.MergeKVs(l.values, kvList)
 	serialize.KVListFormat(buffer, merged...)
 	l.log(LogInfo, msg, level, buffer, nil, kvList)
 }
 
-func (l *tlogger) Enabled(level int) bool {
-	return l.config.vstate.Enabled(verbosity.Level(level), 1)
+func (l tlogger) Enabled(level int) bool {
+	return l.shared.config.vstate.Enabled(verbosity.Level(level), 1)
 }
 
-func (l *tlogger) Error(err error, msg string, kvList ...interface{}) {
-	l.t.Helper()
+func (l tlogger) Error(err error, msg string, kvList ...interface{}) {
+	l.shared.mutex.Lock()
+	defer l.shared.mutex.Unlock()
+	if l.shared.t == nil {
+		l.fallbackLogger().Error(err, msg, kvList...)
+		return
+	}
+
+	l.shared.t.Helper()
 	buffer := &bytes.Buffer{}
 	if err != nil {
 		serialize.KVListFormat(buffer, "err", err)
@@ -265,8 +335,8 @@ func (l *tlogger) Error(err error, msg string, kvList ...interface{}) {
 	l.log(LogError, msg, 0, buffer, err, kvList)
 }
 
-func (l *tlogger) log(what LogType, msg string, level int, buffer *bytes.Buffer, err error, kvList []interface{}) {
-	l.t.Helper()
+func (l tlogger) log(what LogType, msg string, level int, buffer *bytes.Buffer, err error, kvList []interface{}) {
+	l.shared.t.Helper()
 	args := []interface{}{what}
 	if l.prefix != "" {
 		args = append(args, l.prefix+":")
@@ -276,24 +346,24 @@ func (l *tlogger) log(what LogType, msg string, level int, buffer *bytes.Buffer,
 		// Skip leading space inserted by serialize.KVListFormat.
 		args = append(args, string(buffer.Bytes()[1:]))
 	}
-	l.t.Log(args...)
+	l.shared.t.Log(args...)
 
-	l.buffer.mutex.Lock()
-	defer l.buffer.mutex.Unlock()
+	l.shared.buffer.mutex.Lock()
+	defer l.shared.buffer.mutex.Unlock()
 
 	// Store as text.
-	l.buffer.text.WriteString(string(what))
+	l.shared.buffer.text.WriteString(string(what))
 	for i := 1; i < len(args); i++ {
-		l.buffer.text.WriteByte(' ')
-		l.buffer.text.WriteString(args[i].(string))
+		l.shared.buffer.text.WriteByte(' ')
+		l.shared.buffer.text.WriteString(args[i].(string))
 	}
 	lastArg := args[len(args)-1].(string)
 	if lastArg[len(lastArg)-1] != '\n' {
-		l.buffer.text.WriteByte('\n')
+		l.shared.buffer.text.WriteByte('\n')
 	}
 
 	// Store as raw data.
-	l.buffer.log = append(l.buffer.log,
+	l.shared.buffer.log = append(l.shared.buffer.log,
 		LogEntry{
 			Timestamp:       time.Now(),
 			Type:            what,
@@ -310,27 +380,25 @@ func (l *tlogger) log(what LogType, msg string, level int, buffer *bytes.Buffer,
 // WithName returns a new logr.Logger with the specified name appended.  klogr
 // uses '/' characters to separate name elements.  Callers should not pass '/'
 // in the provided name string, but this library does not actually enforce that.
-func (l *tlogger) WithName(name string) logr.LogSink {
-	new := *l
+func (l tlogger) WithName(name string) logr.LogSink {
 	if len(l.prefix) > 0 {
-		new.prefix = l.prefix + "/"
+		l.prefix = l.prefix + "/"
 	}
-	new.prefix += name
-	return &new
+	l.prefix += name
+	return l
 }
 
-func (l *tlogger) WithValues(kvList ...interface{}) logr.LogSink {
-	new := *l
-	new.values = serialize.WithValues(l.values, kvList)
-	return &new
+func (l tlogger) WithValues(kvList ...interface{}) logr.LogSink {
+	l.values = serialize.WithValues(l.values, kvList)
+	return l
 }
 
-func (l *tlogger) GetUnderlying() TL {
-	return l.t
+func (l tlogger) GetUnderlying() TL {
+	return l.shared.t
 }
 
-func (l *tlogger) GetBuffer() Buffer {
-	return l.buffer
+func (l tlogger) GetBuffer() Buffer {
+	return &l.shared.buffer
 }
 
 var _ logr.LogSink = &tlogger{}

ktesting/testinglogger_test.go

@@ -10,9 +10,14 @@ package ktesting_test
 import (
 	"bytes"
 	"errors"
+	"flag"
 	"fmt"
+	"regexp"
+	"runtime"
+	"sync"
 	"testing"
 
+	"k8s.io/klog/v2"
 	"k8s.io/klog/v2/ktesting"
 )
 
@@ -132,6 +137,7 @@ func TestCallDepth(t *testing.T) {
 }
 
 type logToBuf struct {
+	ktesting.NopTL
 	bytes.Buffer
 }
 
@@ -147,3 +153,63 @@ func (l *logToBuf) Log(args ...interface{}) {
 	}
 	l.Write([]byte("\n"))
 }
+
+func TestStop(t *testing.T) {
+	// This test is set up so that a subtest spawns a goroutine and that
+	// goroutine logs through ktesting *after* the subtest has
+	// completed. This is not supported by testing.T.Log and normally
+	// leads to:
+	//   panic: Log in goroutine after TestGoroutines/Sub has completed: INFO hello world
+	//
+	// It works with ktesting if (and only if) logging gets redirected to klog
+	// before returning from the test.
+
+	// Capture output for testing.
+	state := klog.CaptureState()
+	defer state.Restore()
+	var output bytes.Buffer
+	var fs flag.FlagSet
+	klog.InitFlags(&fs)
+	fs.Set("alsologtostderr", "false")
+	fs.Set("logtostderr", "false")
+	fs.Set("stderrthreshold", "FATAL")
+	fs.Set("one_output", "true")
+	klog.SetOutput(&output)
+
+	var line int
+	var wg1, wg2 sync.WaitGroup
+	wg1.Add(1)
+	wg2.Add(1)
+	t.Run("Sub", func(t *testing.T) {
+		logger, _ := ktesting.NewTestContext(t)
+		go func() {
+			defer wg2.Done()
+
+			// Wait for test to have returned.
+			wg1.Wait()
+
+			// This output must go to klog because the test has
+			// completed.
+			_, _, line, _ = runtime.Caller(0)
+			logger.Info("simple info message")
+			logger.Error(nil, "error message")
+			logger.WithName("me").WithValues("completed", true).Info("complex info message", "anotherValue", 1)
+		}()
+	})
+	// Allow goroutine above to proceed.
+	wg1.Done()
+
+	// Ensure that goroutine has completed.
+	wg2.Wait()
+
+	actual := output.String()
+	actual = regexp.MustCompile(`(?m)^.* testinglogger_test.go:`).ReplaceAllString(actual, `testinglogger_test.go:`)
+	expected := fmt.Sprintf(`testinglogger_test.go:%d] "TestStop/Sub leaked goroutine: simple info message"
+testinglogger_test.go:%d] "TestStop/Sub leaked goroutine: error message"
+testinglogger_test.go:%d] "TestStop/Sub leaked goroutine/me: complex info message" completed=true anotherValue=1
+`,
+		line+1, line+2, line+3)
+	if actual != expected {
+		t.Errorf("Output does not match. Expected:\n%s\nActual:\n%s\n", expected, actual)
+	}
+}