tai64n: make the test deterministic

In the presence of preemption, the current test may fail transiently.
This uses static test data instead to ensure consistent behavior.

Signed-off-by: Dmytro Shynkevych <dmytro@tailscale.com>

tai64n/tai64n.go

@@ -17,16 +17,19 @@ const whitenerMask = uint32(0x1000000 - 1)
 
 type Timestamp [TimestampSize]byte
 
-func Now() Timestamp {
+func stamp(t time.Time) Timestamp {
 	var tai64n Timestamp
-	now := time.Now()
-	secs := base + uint64(now.Unix())
-	nano := uint32(now.Nanosecond()) &^ whitenerMask
+	secs := base + uint64(t.Unix())
+	nano := uint32(t.Nanosecond()) &^ whitenerMask
 	binary.BigEndian.PutUint64(tai64n[:], secs)
 	binary.BigEndian.PutUint32(tai64n[8:], nano)
 	return tai64n
 }
 
+func Now() Timestamp {
+	return stamp(time.Now())
+}
+
 func (t1 Timestamp) After(t2 Timestamp) bool {
 	return bytes.Compare(t1[:], t2[:]) > 0
 }