allow setting randomization via flags

allows for setting randomization with flags, but also modifies the
Options struct to now have two separate values

Overall this relates in a much more understandable UI from a user
perspective, since the normal case for randomization will be a user
just saying “run these out of order please” — and in a rare case they
may wish to additionally supply a seed to try to reproduce an older run
to trigger the same error condition.

flags.go

@@ -46,6 +46,8 @@ func FlagSet(opt *Options) *flag.FlagSet {
 	set.BoolVar(&opt.ShowStepDefinitions, "d", false, "Print all available step definitions.")
 	set.BoolVar(&opt.StopOnFailure, "stop-on-failure", false, "Stop processing on first failed scenario.")
 	set.BoolVar(&opt.NoColors, "no-colors", false, "Disable ansi colors.")
+	set.BoolVar(&opt.Randomize, "random", false, "Randomize scenario execution order.")
+	set.Int64Var(&opt.RandomSeed, "seed", 0, "Specify random seed to reproduce shuffling from a previous run.\n(implies --random)")
 	set.Usage = usage(set, opt.Output)
 	return set
 }
@@ -64,7 +66,14 @@ func (f *flagged) name() string {
 	case len(f.short) > 0:
 		name = fmt.Sprintf("-%s", f.short)
 	}
-	if f.dflt != "true" && f.dflt != "false" {
+
+	if f.long == "seed" {
+		// `seed`` is special in that we will later assign it randomly
+		// if the user specifies `--random` without specifying one,
+		// so mask the "default" value here to avoid UI confusion about
+		// what the value will end up being.
+		name += "=SEED"
+	} else if f.dflt != "true" && f.dflt != "false" {
 		name += "=" + f.dflt
 	}
 	return name

options.go

@@ -13,16 +13,22 @@ type Options struct {
 	// Print step definitions found and exit
 	ShowStepDefinitions bool
 
-	// RandomSeed, if not `0`, will be used to run scenarios in a random order.
+	// Randomize causes scenarios to be run in random order.
 	//
 	// Randomizing scenario order is especially helpful for detecting
 	// situations where you have state leaking between scenarios, which can
 	// cause flickering or fragile tests.
+	Randomize bool
+
+	// RandomSeed allows specifying the seed to reproduce the random scenario
+	// shuffling from a previous run.
 	//
-	// The default value of `0` means "do not randomize".
+	// When `RandomSeed` is left at the nil value (`0`), but `Randomize`
+	// has been set to `true`, then godog will automatically pick a random
+	// seed between `1-99999` for ease of specification.
 	//
-	// The magic value of `-1` means "pick a random seed for me", the resulting
-	// seed will only be between `1-99999` for ease of specification.
+	// If RandomSeed is set to anything other than the default nil value (`0`),
+	// then `Randomize = true` will be implied.
 	RandomSeed int64
 
 	// Stops on the first failure

run.go

@@ -111,10 +111,14 @@ func RunWithOptions(suite string, contextInitializer func(suite *Suite), opt Opt
 	features, err := parseFeatures(opt.Tags, opt.Paths)
 	fatal(err)
 
-	seed := opt.RandomSeed
-	if seed == -1 {
-		// if RandomSeed opt is -1, means pick a memorable rand seed as default
-		// the docStrings for Option specify this should be 1-99999 (same as ruby Cucumber)
+	// the actual seed value which will be propogated
+	// if left as nil value, then scenarios run sequentially
+	var seed int64
+	// use specified seed if exists, or assign one ourselves if
+	// none specified but user wants randomization
+	if opt.RandomSeed != 0 {
+		seed = opt.RandomSeed
+	} else if opt.Randomize && opt.RandomSeed == 0 {
 		r := rand.New(rand.NewSource(time.Now().UTC().UnixNano()))
 		seed = r.Int63n(99998) + 1
 	}