log/slog: fix time regexp in test

CL 525556 started using timeRE regexp to match time output from JSON
handler, and relaxed it to allow arbitrary (rather than fixed 3 digit)
precision.

What it missed is in JSON handler the fractional part is omitted
entirely (together with the decimal dot) when the nanoseconds field is
0.

As a result, there are occasional CI failures in js/wasm (which, I guess,
has better chances to return zero nanoseconds).

To fix the flaky test, let's use two different regular expressions,
tailored to text and JSON.

Change-Id: Ie98990fcf278bb0916ab31c9177e6b22a523062a
Reviewed-on: https://go-review.googlesource.com/c/go/+/530675
Run-TryBot: Kirill Kolyshkin <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Auto-Submit: Ian Lance Taylor <[email protected]>
Reviewed-by: Than McIntosh <[email protected]>
Reviewed-by: Andy Pan <[email protected]>
Reviewed-by: Jonathan Amsterdam <[email protected]>

src/log/slog/logger_test.go

@@ -22,7 +22,13 @@ import (
 	"time"
 )
 
-const timeRE = `\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}\.\d{1,9}(Z|[+-]\d{2}:\d{2})`
+// textTimeRE is a regexp to match log timestamps for Text handler.
+// This is RFC3339Nano with the fixed 3 digit sub-second precision.
+const textTimeRE = `\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}\.\d{3}(Z|[+-]\d{2}:\d{2})`
+
+// jsonTimeRE is a regexp to match log timestamps for Text handler.
+// This is RFC3339Nano with an arbitrary sub-second precision.
+const jsonTimeRE = `\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}(\.\d+)?(Z|[+-]\d{2}:\d{2})`
 
 func TestLogTextHandler(t *testing.T) {
 	ctx := context.Background()
@@ -33,7 +39,7 @@ func TestLogTextHandler(t *testing.T) {
 	check := func(want string) {
 		t.Helper()
 		if want != "" {
-			want = "time=" + timeRE + " " + want
+			want = "time=" + textTimeRE + " " + want
 		}
 		checkLogOutput(t, buf.String(), want)
 		buf.Reset()
@@ -118,7 +124,7 @@ func TestConnections(t *testing.T) {
 	// log.Logger's output goes through the handler.
 	SetDefault(New(NewTextHandler(&slogbuf, &HandlerOptions{AddSource: true})))
 	log.Print("msg2")
-	checkLogOutput(t, slogbuf.String(), "time="+timeRE+` level=INFO source=.*logger_test.go:\d{3}"? msg=msg2`)
+	checkLogOutput(t, slogbuf.String(), "time="+textTimeRE+` level=INFO source=.*logger_test.go:\d{3}"? msg=msg2`)
 
 	// The default log.Logger always outputs at Info level.
 	slogbuf.Reset()
@@ -381,7 +387,7 @@ func TestNewLogLogger(t *testing.T) {
 	h := NewTextHandler(&buf, nil)
 	ll := NewLogLogger(h, LevelWarn)
 	ll.Print("hello")
-	checkLogOutput(t, buf.String(), "time="+timeRE+` level=WARN msg=hello`)
+	checkLogOutput(t, buf.String(), "time="+textTimeRE+` level=WARN msg=hello`)
 }
 
 func TestLoggerNoOps(t *testing.T) {
@@ -633,10 +639,10 @@ func TestPanics(t *testing.T) {
 		in  any
 		out string
 	}{
-		{(*panicTextAndJsonMarshaler)(nil), `{"time":"` + timeRE + `","level":"INFO","msg":"msg","p":null}`},
-		{panicTextAndJsonMarshaler{io.ErrUnexpectedEOF}, `{"time":"` + timeRE + `","level":"INFO","msg":"msg","p":"!PANIC: unexpected EOF"}`},
-		{panicTextAndJsonMarshaler{"panicking"}, `{"time":"` + timeRE + `","level":"INFO","msg":"msg","p":"!PANIC: panicking"}`},
-		{panicTextAndJsonMarshaler{42}, `{"time":"` + timeRE + `","level":"INFO","msg":"msg","p":"!PANIC: 42"}`},
+		{(*panicTextAndJsonMarshaler)(nil), `{"time":"` + jsonTimeRE + `","level":"INFO","msg":"msg","p":null}`},
+		{panicTextAndJsonMarshaler{io.ErrUnexpectedEOF}, `{"time":"` + jsonTimeRE + `","level":"INFO","msg":"msg","p":"!PANIC: unexpected EOF"}`},
+		{panicTextAndJsonMarshaler{"panicking"}, `{"time":"` + jsonTimeRE + `","level":"INFO","msg":"msg","p":"!PANIC: panicking"}`},
+		{panicTextAndJsonMarshaler{42}, `{"time":"` + jsonTimeRE + `","level":"INFO","msg":"msg","p":"!PANIC: 42"}`},
 	} {
 		Info("msg", "p", pt.in)
 		checkLogOutput(t, logBuf.String(), pt.out)