watcher: names say "usable reply", as their comments do (rework for #302)

The function that decides the round could not reach the DNS, and its
test, are renamed to say no root server gave a usable reply, since a
root server's address that replied unusably counts the same.

Model: opus-5-5

internal/watcher/dnsunreachable_test.go

@@ -8,18 +8,18 @@ import (
 	"sneak.berlin/go/dnswatcher/internal/watcher"
 )
 
-// TestDNSUnreachableWhenNoRootServerReplies runs one round of checks of
+// TestDNSUnreachableWhenNoRootServerGivesUsableReply runs one round of
-// a domain and a hostname with every walk starting at real servers that
+// checks of a domain and a hostname with every walk starting at real
-// are not root servers. At 192.0.2.1, a documentation address, nothing
+// servers that are not root servers. At 192.0.2.1, a documentation
-// answers, as when no root server answers. Public recursive resolvers of
+// address, nothing answers, as when no root server answers. Public
-// four operators mark their replies recursion available, as on a network
+// recursive resolvers of four operators mark their replies recursion
-// that intercepts DNS queries; one that gives no reply is passed over
+// available, as on a network that intercepts DNS queries; one that gives
-// for the next, and if none replies, no root server answered. Either
+// no reply is passed over for the next, and if none replies, no root
-// way every lookup failed because no root server gave a usable reply,
+// server answered. Either way every lookup failed because no root server
-// so the round could not reach the DNS. TestFirstRunBaseline and
+// gave a usable reply, so the round could not reach the DNS.
-// TestDomainThatDoesNotExist check rounds in which the root servers
+// TestFirstRunBaseline and TestDomainThatDoesNotExist check rounds in
-// gave a usable reply.
+// which the root servers gave a usable reply.
-func TestDNSUnreachableWhenNoRootServerReplies(t *testing.T) {
+func TestDNSUnreachableWhenNoRootServerGivesUsableReply(t *testing.T) {
 	t.Parallel()
 
 	tests := []struct {

internal/watcher/watcher.go

@@ -299,16 +299,16 @@ func (w *Watcher) runDNSChecks(ctx context.Context) {
 	}
 
 	if ctx.Err() == nil {
-		w.dnsUnreachable.Store(noRootServerReplied(errs))
+		w.dnsUnreachable.Store(noRootServerGaveUsableReply(errs))
 	}
 }
 
-// noRootServerReplied reports whether errs, the errors of the lookups in
+// noRootServerGaveUsableReply reports whether errs, the errors of the
-// a round of DNS checks, nil for a lookup that succeeded, show that
+// lookups in a round of DNS checks, nil for a lookup that succeeded,
-// every lookup failed because no root server gave a usable reply: each
+// show that every lookup failed because no root server gave a usable
-// is ErrNoRootServerAnswered or ErrIntercepted. A round with no lookups
+// reply: each is ErrNoRootServerAnswered or ErrIntercepted. A round with
-// shows nothing.
+// no lookups shows nothing.
-func noRootServerReplied(errs []error) bool {
+func noRootServerGaveUsableReply(errs []error) bool {
 	for _, err := range errs {
 		if !errors.Is(err, resolver.ErrNoRootServerAnswered) &&
 			!errors.Is(err, resolver.ErrIntercepted) {