func parse(s string) time.Time {
	t, err := time.Parse("Mon Jan  2 15:04:05 PST 2006", s)
	if err != nil {
		panic(err)
	}
	return t
}
parse returns a time formatted as the standard output of "date", e.g.:
Thu Dec 17 15:18:30 PST 2015
package cal_test
import (
	"testing"
	"time"
	"github.com/Netflix/chaosmonkey/cal"
)
var weekdayTests = []struct {
	date string
	pred bool
}{
	{"Mon Dec 14 11:33:58 PST 2015", true},
	{"Tue Dec 15 11:33:58 PST 2015", true},
	{"Wed Dec 16 11:33:58 PST 2015", true},
	{"Thu Dec 17 11:33:58 PST 2015", true},
	{"Fri Dec 18 11:33:58 PST 2015", true},
	{"Sat Dec 19 11:33:58 PST 2015", false},
	{"Sun Dec 20 11:33:58 PST 2015", false},
}
func TestIsWorkday(t *testing.T) {
	for _, tt := range weekdayTests {
		if got, want := cal.IsWorkday(parse(tt.date)), tt.pred; got != want {
			t.Fatalf("isWeekday(\"%s\")=%t, want %t", tt.date, got, want)
		}
	}
}