func (t *Test) parseLoad(lines []string, i int) (int, *loadCmd, error) {
	if !patLoad.MatchString(lines[i]) {
		return i, nil, raise(i, "invalid load command. (load <step:duration>)")
	}
	parts := patLoad.FindStringSubmatch(lines[i])

	gap, err := strutil.StringToDuration(parts[1])
	if err != nil {
		return i, nil, raise(i, "invalid step definition %q: %s", parts[1], err)
	}
	cmd := newLoadCmd(gap)
	for i+1 < len(lines) {
		i++
		defLine := lines[i]
		if len(defLine) == 0 {
			i--
			break
		}
		metric, vals, err := parseSeriesDesc(defLine)
		if err != nil {
			perr := err.(*ParseErr)
			perr.Line = i + 1
			return i, nil, err
		}
		cmd.set(metric, vals...)
	}
	return i, cmd, nil
}

func (t *Test) parseEval(lines []string, i int) (int, *evalCmd, error) {
	if !patEvalInstant.MatchString(lines[i]) {
		return i, nil, raise(i, "invalid evaluation command. (eval[_fail|_ordered] instant [at <offset:duration>] <query>")
	}
	parts := patEvalInstant.FindStringSubmatch(lines[i])
	var (
		mod = parts[1]
		at  = parts[2]
		qry = parts[3]
	)
	expr, err := ParseExpr(qry)
	if err != nil {
		if perr, ok := err.(*ParseErr); ok {
			perr.Line = i + 1
			perr.Pos += strings.Index(lines[i], qry)
		}
		return i, nil, err
	}

	offset, err := strutil.StringToDuration(at)
	if err != nil {
		return i, nil, raise(i, "invalid step definition %q: %s", parts[1], err)
	}
	ts := testStartTime.Add(offset)

	cmd := newEvalCmd(expr, ts, ts, 0)
	switch mod {
	case "ordered":
		cmd.ordered = true
	case "fail":
		cmd.fail = true
	}

	for j := 1; i+1 < len(lines); j++ {
		i++
		defLine := lines[i]
		if len(defLine) == 0 {
			i--
			break
		}
		if f, err := parseNumber(defLine); err == nil {
			cmd.expect(0, nil, sequenceValue{value: clientmodel.SampleValue(f)})
			break
		}
		metric, vals, err := parseSeriesDesc(defLine)
		if err != nil {
			if perr, ok := err.(*ParseErr); ok {
				perr.Line = i + 1
			}
			return i, nil, err
		}

		// Currently, we are not expecting any matrices.
		if len(vals) > 1 {
			return i, nil, raise(i, "expecting multiple values in instant evaluation not allowed")
		}
		cmd.expect(j, metric, vals...)
	}
	return i, cmd, nil
}

func parseDuration(s string) (time.Duration, error) {
	if d, err := strconv.ParseFloat(s, 64); err == nil {
		return time.Duration(d * float64(time.Second)), nil
	}
	if d, err := strutil.StringToDuration(s); err == nil {
		return d, nil
	}
	return 0, fmt.Errorf("cannot parse %q to a valid duration", s)
}

func parseDuration(ds string) (time.Duration, error) {
	dur, err := strutil.StringToDuration(ds)
	if err != nil {
		return 0, err
	}
	if dur == 0 {
		return 0, fmt.Errorf("duration must be greater than 0")
	}
	return dur, nil
}

// UnmarshalYAML implements the yaml.Unmarshaler interface.
func (d *Duration) UnmarshalYAML(unmarshal func(interface{}) error) error {
	var s string
	if err := unmarshal(&s); err != nil {
		return err
	}
	dur, err := strutil.StringToDuration(s)
	if err != nil {
		return err
	}
	*d = Duration(dur)
	return nil
}