command: add Covers() for attenuation test, fix incorrect Segments()

pkg/command/command.go

@@ -98,7 +98,24 @@ func (c Command) Join(segments ...string) Command {
 // Segments returns the ordered segments that comprise the Command as a
 // slice of strings.
 func (c Command) Segments() []string {
-	return strings.Split(string(c), separator)
+	if c == separator {
+		return nil
+	}
+	return strings.Split(string(c), separator)[1:]
+}
+
+// Covers returns true if the command is identical or a parent of the given other command.
+func (c Command) Covers(other Command) bool {
+	otherSegments := other.Segments()
+	if len(otherSegments) < len(c.Segments()) {
+		return false
+	}
+	for i, s := range c.Segments() {
+		if otherSegments[i] != s {
+			return false
+		}
+	}
+	return true
 }
 
 // String returns the composed representation the command.  This is also