For example, 

--- PASS: TestConnectionlessWriteTooLongError (0.00 seconds)
    write_test.go:89: 65536 bytes write udp4: message too long
    write_test.go:110: 65536 bytes write udp4: message too long
    write_test.go:89: 65536 bytes write udp6: message too long
    write_test.go:110: 65536 bytes write udp6: message too long
    write_test.go:89: 1048576 bytes write unixgram: message too long
    write_test.go:110: 1048576 bytes write unixgram: message too long

instead of

--- PASS: TestConnectionlessWriteTooLongError (0.00 seconds)
    write_test.go:89: 65536 bytes write udp4 127.0.0.1:33494: message too long
    write_test.go:110: 65536 bytes write udp4 127.0.0.1:33494: message too long
    write_test.go:89: 65536 bytes write udp6 [::1]:42353: message too long
    write_test.go:110: 65536 bytes write udp6 [::1]:42353: message too long
    write_test.go:89: 1048576 bytes write unixgram /tmp/nettest925274809:: message too long
    write_test.go:110: 1048576 bytes write unixgram /tmp/nettest925274809:: message too long

The root cause is issue #4856.