ktesting: capture log entries only if requested

Most users won't need this feature. It was enabled by default to keep the API
simple and because the primary goal was unit testing, but benchmarks also need
this and there unnecessary overhead needs to be avoided.

ktesting/example_test.go

@@ -25,7 +25,7 @@ import (
 )
 
 func ExampleUnderlier() {
-	logger := ktesting.NewLogger(ktesting.NopTL{}, ktesting.NewConfig(ktesting.Verbosity(4)))
+	logger := ktesting.NewLogger(ktesting.NopTL{}, ktesting.NewConfig(ktesting.Verbosity(4), ktesting.BufferLogs(true)))
 
 	logger.Error(errors.New("failure"), "I failed", "what", "something")
 	logger.WithValues("request", 42).WithValues("anotherValue", "fish").Info("hello world")

ktesting/options.go

@@ -50,6 +50,7 @@ type configOptions struct {
 	verbosityFlagName string
 	vmoduleFlagName   string
 	verbosityDefault  int
+	bufferLogs        bool
 }
 
 // VerbosityFlagName overrides the default -testing.v for the verbosity level.
@@ -94,6 +95,21 @@ func Verbosity(level int) ConfigOption {
 	}
 }
 
+// BufferLogs controlls whether log entries are captured in memory in addition
+// to being printed. Off by default. Unit tests that want to verify that
+// log entries are emitted as expected can turn this on and then retrieve
+// the captured log through the Underlier LogSink interface.
+//
+// # Experimental
+//
+// Notice: This function is EXPERIMENTAL and may be changed or removed in a
+// later release.
+func BufferLogs(enabled bool) ConfigOption {
+	return func(co *configOptions) {
+		co.bufferLogs = enabled
+	}
+}
+
 // NewConfig returns a configuration with recommended defaults and optional
 // modifications. Command line flags are not bound to any FlagSet yet.
 //

ktesting/testinglogger.go

@@ -376,6 +376,10 @@ func (l tlogger) log(what LogType, msg string, level int, buf *buffer.Buffer, er
 		l.shared.buffer.text.WriteByte('\n')
 	}
 
+	if !l.shared.config.co.bufferLogs {
+		return
+	}
+
 	// Store as raw data.
 	l.shared.buffer.log = append(l.shared.buffer.log,
 		LogEntry{