test: Add small miscellaneous tests

This patch extends various packages and integration tests, increasing
test coverage. They're small enough that it's not worth splitting them
up, as it would add a lot of noise to the history.

internal/queue/queue.go

@@ -30,7 +30,6 @@ import (
 	"blitiri.com.ar/go/log"
 
 	"github.com/golang/protobuf/ptypes"
-	"github.com/golang/protobuf/ptypes/timestamp"
 	"golang.org/x/net/idna"
 )
 
@@ -481,12 +480,6 @@ func nextDelay(createdAt time.Time) time.Duration {
 	return delay
 }
 
-func timestampNow() *timestamp.Timestamp {
-	now := time.Now()
-	ts, _ := ptypes.TimestampProto(now)
-	return ts
-}
-
 func mustIDNAToASCII(s string) string {
 	a, err := idna.ToASCII(s)
 	if err != nil {