time: update TestSub to avoid future regressions

CL 131196 optimized Time.Sub, but was reverted because
it incorrectly computed the nanoseconds in some edge cases.
This CL adds a test case to enforce the correct behavior
so that a future optimization does not break this again.

Updates #17858
Updates #33677

Change-Id: I596d8302ca6bf721cf7ca11cc6f939639fcbdd43
Reviewed-on: https://go-review.googlesource.com/c/go/+/190524
Run-TryBot: Joe Tsai <thebrokentoaster@gmail.com>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Reviewed-by: Andrew Bonventre <andybons@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/time/time_test.go

@@ -690,7 +690,7 @@ var gobTests = []Time{
 	Date(0, 1, 2, 3, 4, 5, 6, UTC),
 	Date(7, 8, 9, 10, 11, 12, 13, FixedZone("", 0)),
 	Unix(81985467080890095, 0x76543210), // Time.sec: 0x0123456789ABCDEF
-	{}, // nil location
+	{},                                  // nil location
 	Date(1, 2, 3, 4, 5, 6, 7, FixedZone("", 32767*60)),
 	Date(1, 2, 3, 4, 5, 6, 7, FixedZone("", -32768*60)),
 }
@@ -995,6 +995,7 @@ var subTests = []struct {
 	{Date(2300, 1, 1, 0, 0, 0, 0, UTC), Date(2000, 1, 1, 0, 0, 0, 0, UTC), Duration(maxDuration)},
 	{Date(2000, 1, 1, 0, 0, 0, 0, UTC), Date(2290, 1, 1, 0, 0, 0, 0, UTC), -290*365*24*Hour - 71*24*Hour},
 	{Date(2000, 1, 1, 0, 0, 0, 0, UTC), Date(2300, 1, 1, 0, 0, 0, 0, UTC), Duration(minDuration)},
+	{Date(2311, 11, 26, 02, 16, 47, 63535996, UTC), Date(2019, 8, 16, 2, 29, 30, 268436582, UTC), 9223372036795099414},
 	{MinMonoTime, MaxMonoTime, minDuration},
 	{MaxMonoTime, MinMonoTime, maxDuration},
 }