Merge pull request #364 from cucumber/allow_empty_return_step

feat(step_definition): Allows to define step function without return.
2021-07-22 20:59:48 +02:00 · 2021-07-22 20:59:48 +02:00 · 15358d20e7
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@ -12,6 +12,8 @@ This document is formatted according to the principles of [Keep A CHANGELOG](htt

 ### Added

+* Support for step definitions without return ([364](https://github.com/cucumber/godog/pull/364) -[titouanfreville])
+
 ### Changed

 * Upgraded gherkin-go to v19 ([402](https://github.com/cucumber/godog/pull/402) - [mbow])
--- a/README.md
+++ b/README.md
@ -210,6 +210,14 @@ Feature: eat godogs

 You may change **return godog.ErrPending** to **return nil** in the three step definitions and the scenario will pass successfully.

+Also, you may omit error return if your step does not fail.
+
+```go
+func iEat(arg1 int) {
+	// Eat arg1.
+}
+```
+
 #### Step 5 - Create the main program to test

 We only need a number of **godogs** for now. Lets keep it simple.
--- a/features/tags.feature
+++ b/features/tags.feature
@ -10,6 +10,7 @@ Feature: tag filters

        Background:
          Given passing step
+          And passing step without return

        Scenario Outline: parse a scenario
          Given a feature path "<path>"
--- a/go.mod
+++ b/go.mod
@ -7,6 +7,7 @@ require (
 	github.com/cucumber/messages-go/v16 v16.0.1
 	github.com/hashicorp/go-memdb v1.3.0
 	github.com/hashicorp/go-uuid v1.0.2 // indirect
+	github.com/smartystreets/goconvey v1.6.4
 	github.com/spf13/cobra v1.1.1
 	github.com/spf13/pflag v1.0.5
 	github.com/stretchr/testify v1.7.0
--- a/go.sum
+++ b/go.sum
@ -71,6 +71,7 @@ github.com/google/pprof v0.0.0-20190515194954-54271f7e092f/go.mod h1:zfwlbNMJ+OI
 github.com/google/renameio v0.1.0/go.mod h1:KWCgfxg9yswjAJkECMjeO8J8rahYeXnNhOm40UhjYkI=
 github.com/googleapis/gax-go/v2 v2.0.4/go.mod h1:0Wqv26UfaUD9n4G6kQubkQ+KchISgw+vpHVxEJEs9eg=
 github.com/googleapis/gax-go/v2 v2.0.5/go.mod h1:DWXyrwAJ9X0FpwwEdw+IPEYBICEFu5mhpdKc/us6bOk=
+github.com/gopherjs/gopherjs v0.0.0-20181017120253-0766667cb4d1 h1:EGx4pi6eqNxGaHF6qqu48+N2wcFQ5qg5FXgOdqsJ5d8=
 github.com/gopherjs/gopherjs v0.0.0-20181017120253-0766667cb4d1/go.mod h1:wJfORRmW1u3UXTncJ5qlYoELFm8eSnnEO6hX4iZ3EWY=
 github.com/gorilla/websocket v1.4.2/go.mod h1:YR8l580nyteQvAITg2hZ9XVh4b55+EU/adAjf1fMHhE=
 github.com/grpc-ecosystem/go-grpc-middleware v1.0.0/go.mod h1:FiyG127CGDf3tlThmgyCl78X/SZQqEOJBCDaAfeWzPs=
@ -109,6 +110,7 @@ github.com/inconshreveable/mousetrap v1.0.0/go.mod h1:PxqpIevigyE2G7u3NXJIT2ANyt
 github.com/jonboulle/clockwork v0.1.0/go.mod h1:Ii8DK3G1RaLaWxj9trq07+26W01tbo22gdxWY5EU2bo=
 github.com/json-iterator/go v1.1.6/go.mod h1:+SdeFBvtyEkXs7REEP0seUULqWtbJapLOCVDaaPEHmU=
 github.com/jstemmer/go-junit-report v0.0.0-20190106144839-af01ea7f8024/go.mod h1:6v2b51hI/fHJwM22ozAgKL4VKDeJcHhJFhtBdhmNjmU=
+github.com/jtolds/gls v4.20.0+incompatible h1:xdiiI2gbIgH/gLH7ADydsJ1uDOEzR8yvV7C0MuV77Wo=
 github.com/jtolds/gls v4.20.0+incompatible/go.mod h1:QJZ7F/aHp+rZTRtaJ1ow/lLfFfVYBRgL+9YlvaHOwJU=
 github.com/julienschmidt/httprouter v1.2.0/go.mod h1:SYymIcj16QtmaHHD7aYtjjsJG7VTCxuUUipMqKk8s4w=
 github.com/kisielk/errcheck v1.1.0/go.mod h1:EZBBE59ingxPouuu3KfxchcWSUPOHkagtvWXihfKN4Q=
@ -161,7 +163,9 @@ github.com/ryanuber/columnize v0.0.0-20160712163229-9b3edd62028f/go.mod h1:sm1tb
 github.com/sean-/seed v0.0.0-20170313163322-e2103e2c3529/go.mod h1:DxrIzT+xaE7yg65j358z/aeFdxmN0P9QXhEzd20vsDc=
 github.com/shurcooL/sanitized_anchor_name v1.0.0/go.mod h1:1NzhyTcUVG4SuEtjjoZeVRXNmyL/1OwPU0+IJeTBvfc=
 github.com/sirupsen/logrus v1.2.0/go.mod h1:LxeOpSwHxABJmUn/MG1IvRgCAasNZTLOkJPxbbu5VWo=
+github.com/smartystreets/assertions v0.0.0-20180927180507-b2de0cb4f26d h1:zE9ykElWQ6/NYmHa3jpm/yHnI4xSofP+UP6SpjHcSeM=
 github.com/smartystreets/assertions v0.0.0-20180927180507-b2de0cb4f26d/go.mod h1:OnSkiWE9lh6wB0YB77sQom3nweQdgAjqCqsofrRNTgc=
+github.com/smartystreets/goconvey v1.6.4 h1:fv0U8FUIMPNf1L9lnHLvLhgicrIVChEkdzIKYqbNC9s=
 github.com/smartystreets/goconvey v1.6.4/go.mod h1:syvi0/a8iFYH4r/RixwvyeAJjdLS9QV7WQ/tjFTllLA=
 github.com/soheilhy/cmux v0.1.4/go.mod h1:IM3LyeVVIOuxMH7sFAkER9+bJ4dT7Ms6E4xg4kGIyLM=
 github.com/spaolacci/murmur3 v0.0.0-20180118202830-f09979ecbc72/go.mod h1:JwIasOWyU6f++ZhiEuf87xNszmSA2myDM2Kzu9HwQUA=
--- a/internal/models/stepdef.go
+++ b/internal/models/stepdef.go
@ -1,6 +1,7 @@
 package models

 import (
+	"errors"
 	"fmt"
 	"reflect"
 	"strconv"
@ -12,6 +13,13 @@ import (

 var typeOfBytes = reflect.TypeOf([]byte(nil))

+// matchable errors
+var (
+	ErrUnmatchedStepArgumentNumber = errors.New("func received more arguments than expected")
+	ErrCannotConvert               = errors.New("cannot convert argument")
+	ErrUnsupportedArgumentType     = errors.New("unsupported argument type")
+)
+
 // StepDefinition ...
 type StepDefinition struct {
 	formatters.StepDefinition
@ -28,8 +36,9 @@ type StepDefinition struct {
 func (sd *StepDefinition) Run() interface{} {
 	typ := sd.HandlerValue.Type()
 	if len(sd.Args) < typ.NumIn() {
-		return fmt.Errorf("func expects %d arguments, which is more than %d matched from step", typ.NumIn(), len(sd.Args))
+		return fmt.Errorf("%w: expected %d arguments, matched %d from step", ErrUnmatchedStepArgumentNumber, typ.NumIn(), len(sd.Args))
 	}
+
 	var values []reflect.Value
 	for i := 0; i < typ.NumIn(); i++ {
 		param := typ.In(i)
@ -41,7 +50,7 @@ func (sd *StepDefinition) Run() interface{} {
 			}
 			v, err := strconv.ParseInt(s, 10, 0)
 			if err != nil {
-				return fmt.Errorf(`cannot convert argument %d: "%s" to int: %s`, i, s, err)
+				return fmt.Errorf(`%w %d: "%s" to int: %s`, ErrCannotConvert, i, s, err)
 			}
 			values = append(values, reflect.ValueOf(int(v)))
 		case reflect.Int64:
@ -51,9 +60,9 @@ func (sd *StepDefinition) Run() interface{} {
 			}
 			v, err := strconv.ParseInt(s, 10, 64)
 			if err != nil {
-				return fmt.Errorf(`cannot convert argument %d: "%s" to int64: %s`, i, s, err)
+				return fmt.Errorf(`%w %d: "%s" to int64: %s`, ErrCannotConvert, i, s, err)
 			}
-			values = append(values, reflect.ValueOf(int64(v)))
+			values = append(values, reflect.ValueOf(v))
 		case reflect.Int32:
 			s, err := sd.shouldBeString(i)
 			if err != nil {
@ -61,7 +70,7 @@ func (sd *StepDefinition) Run() interface{} {
 			}
 			v, err := strconv.ParseInt(s, 10, 32)
 			if err != nil {
-				return fmt.Errorf(`cannot convert argument %d: "%s" to int32: %s`, i, s, err)
+				return fmt.Errorf(`%w %d: "%s" to int32: %s`, ErrCannotConvert, i, s, err)
 			}
 			values = append(values, reflect.ValueOf(int32(v)))
 		case reflect.Int16:
@ -71,7 +80,7 @@ func (sd *StepDefinition) Run() interface{} {
 			}
 			v, err := strconv.ParseInt(s, 10, 16)
 			if err != nil {
-				return fmt.Errorf(`cannot convert argument %d: "%s" to int16: %s`, i, s, err)
+				return fmt.Errorf(`%w %d: "%s" to int16: %s`, ErrCannotConvert, i, s, err)
 			}
 			values = append(values, reflect.ValueOf(int16(v)))
 		case reflect.Int8:
@ -81,7 +90,7 @@ func (sd *StepDefinition) Run() interface{} {
 			}
 			v, err := strconv.ParseInt(s, 10, 8)
 			if err != nil {
-				return fmt.Errorf(`cannot convert argument %d: "%s" to int8: %s`, i, s, err)
+				return fmt.Errorf(`%w %d: "%s" to int8: %s`, ErrCannotConvert, i, s, err)
 			}
 			values = append(values, reflect.ValueOf(int8(v)))
 		case reflect.String:
@ -97,7 +106,7 @@ func (sd *StepDefinition) Run() interface{} {
 			}
 			v, err := strconv.ParseFloat(s, 64)
 			if err != nil {
-				return fmt.Errorf(`cannot convert argument %d: "%s" to float64: %s`, i, s, err)
+				return fmt.Errorf(`%w %d: "%s" to float64: %s`, ErrCannotConvert, i, s, err)
 			}
 			values = append(values, reflect.ValueOf(v))
 		case reflect.Float32:
@ -107,7 +116,7 @@ func (sd *StepDefinition) Run() interface{} {
 			}
 			v, err := strconv.ParseFloat(s, 32)
 			if err != nil {
-				return fmt.Errorf(`cannot convert argument %d: "%s" to float32: %s`, i, s, err)
+				return fmt.Errorf(`%w %d: "%s" to float32: %s`, ErrCannotConvert, i, s, err)
 			}
 			values = append(values, reflect.ValueOf(float32(v)))
 		case reflect.Ptr:
@ -124,7 +133,7 @@ func (sd *StepDefinition) Run() interface{} {
 					break
 				}

-				return fmt.Errorf(`cannot convert argument %d: "%v" of type "%T" to *messages.PickleStepArgument_PickleDocString`, i, arg, arg)
+				return fmt.Errorf(`%w %d: "%v" of type "%T" to *messages.PickleDocString`, ErrCannotConvert, i, arg, arg)
 			case "messages.PickleTable":
 				if v, ok := arg.(*messages.PickleStepArgument); ok {
 					values = append(values, reflect.ValueOf(v.DataTable))
@ -136,9 +145,9 @@ func (sd *StepDefinition) Run() interface{} {
 					break
 				}

-				return fmt.Errorf(`cannot convert argument %d: "%v" of type "%T" to *messages.PickleStepArgument_PickleTable`, i, arg, arg)
+				return fmt.Errorf(`%w %d: "%v" of type "%T" to *messages.PickleStepArgument_PickleTable`, ErrCannotConvert, i, arg, arg)
 			default:
-				return fmt.Errorf("the argument %d type %T is not supported %s", i, arg, param.Elem().String())
+				return fmt.Errorf("%w: the argument %d type %T is not supported %s", ErrUnsupportedArgumentType, i, arg, param.Elem().String())
 			}
 		case reflect.Slice:
 			switch param {
@ -149,14 +158,19 @@ func (sd *StepDefinition) Run() interface{} {
 				}
 				values = append(values, reflect.ValueOf([]byte(s)))
 			default:
-				return fmt.Errorf("the slice argument %d type %s is not supported", i, param.Kind())
+				return fmt.Errorf("%w: the slice argument %d type %s is not supported", ErrUnsupportedArgumentType, i, param.Kind())
 			}
 		default:
-			return fmt.Errorf("the argument %d type %s is not supported", i, param.Kind())
+			return fmt.Errorf("%w: the argument %d type %s is not supported", ErrUnsupportedArgumentType, i, param.Kind())
 		}
 	}

-	return sd.HandlerValue.Call(values)[0].Interface()
+	res := sd.HandlerValue.Call(values)
+	if len(res) == 0 {
+		return nil
+	}
+
+	return res[0].Interface()
 }

 func (sd *StepDefinition) shouldBeString(idx int) (string, error) {
@ -166,13 +180,13 @@ func (sd *StepDefinition) shouldBeString(idx int) (string, error) {
 		return arg, nil
 	case *messages.PickleStepArgument:
 		if arg.DocString == nil {
-			return "", fmt.Errorf(`cannot convert DocString is not set`)
+			return "", fmt.Errorf(`%w %d: "%v" of type "%T": DocString is not set`, ErrCannotConvert, idx, arg, arg)
 		}
 		return arg.DocString.Content, nil
 	case *messages.PickleDocString:
 		return arg.Content, nil
 	default:
-		return "", fmt.Errorf(`cannot convert argument %d: "%v" of type "%T" to string`, idx, arg, arg)
+		return "", fmt.Errorf(`%w %d: "%v" of type "%T" to string`, ErrCannotConvert, idx, arg, arg)
 	}
 }

--- a/internal/models/stepdef_test.go
+++ b/internal/models/stepdef_test.go
@ -1,6 +1,7 @@
 package models_test

 import (
+	"errors"
 	"fmt"
 	"reflect"
 	"strings"
@ -8,10 +9,32 @@ import (

 	"github.com/cucumber/messages-go/v16"

+	"github.com/cucumber/godog"
 	"github.com/cucumber/godog/formatters"
 	"github.com/cucumber/godog/internal/models"
 )

+func TestShouldSupportEmptyHandlerReturn(t *testing.T) {
+	fn := func(a int64, b int32, c int16, d int8) {}
+
+	def := &models.StepDefinition{
+		StepDefinition: formatters.StepDefinition{
+			Handler: fn,
+		},
+		HandlerValue: reflect.ValueOf(fn),
+	}
+
+	def.Args = []interface{}{"1", "1", "1", "1"}
+	if err := def.Run(); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	def.Args = []interface{}{"1", "1", "1", strings.Repeat("1", 9)}
+	if err := def.Run(); err == nil {
+		t.Fatalf("expected convertion fail for int8, but got none")
+	}
+}
+
 func TestShouldSupportIntTypes(t *testing.T) {
 	fn := func(a int64, b int32, c int16, d int8) error { return nil }

@ -132,23 +155,178 @@ func TestUnexpectedArguments(t *testing.T) {
 	}

 	def.Args = []interface{}{"1"}
-	if err := def.Run(); err == nil {
+
+	res := def.Run()
+	if res == nil {
 		t.Fatalf("expected an error due to wrong number of arguments, but got none")
 	}

-	def.Args = []interface{}{"one", "two"}
-	if err := def.Run(); err == nil {
-		t.Fatalf("expected conversion error, but got none")
+	err, ok := res.(error)
+	if !ok {
+		t.Fatalf("expected an error due to wrong number of arguments, but got %T instead", res)
 	}

-	// @TODO maybe we should support duration
-	// fn2 := func(err time.Duration) error { return nil }
-	// def = &models.StepDefinition{Handler: fn2, HandlerValue: reflect.ValueOf(fn2)}
+	if !errors.Is(err, models.ErrUnmatchedStepArgumentNumber) {
+		t.Fatalf("expected an error due to wrong number of arguments, but got %v instead", err)
+	}
+}

-	// def.Args = []interface{}{"1"}
-	// if err := def.Run(); err == nil {
-	// 	t.Fatalf("expected an error due to wrong argument type, but got none")
-	// }
+func TestStepDefinition_Run_StepShouldBeString(t *testing.T) {
+	test := func(t *testing.T, fn interface{}) {
+		def := &models.StepDefinition{
+			StepDefinition: formatters.StepDefinition{
+				Handler: fn,
+			},
+			HandlerValue: reflect.ValueOf(fn),
+		}
+
+		def.Args = []interface{}{12}
+
+		res := def.Run()
+		if res == nil {
+			t.Fatalf("expected a string convertion error, but got none")
+		}
+
+		err, ok := res.(error)
+		if !ok {
+			t.Fatalf("expected a string convertion error, but got %T instead", res)
+		}
+
+		if !errors.Is(err, models.ErrCannotConvert) {
+			t.Fatalf("expected a string convertion error, but got '%v' instead", err)
+		}
+	}
+
+	// Ensure step type error if step argument is not a string
+	// for all supported types.
+	test(t, func(a int) error { return nil })
+	test(t, func(a int64) error { return nil })
+	test(t, func(a int32) error { return nil })
+	test(t, func(a int16) error { return nil })
+	test(t, func(a int8) error { return nil })
+	test(t, func(a string) error { return nil })
+	test(t, func(a float64) error { return nil })
+	test(t, func(a float32) error { return nil })
+	test(t, func(a *godog.Table) error { return nil })
+	test(t, func(a *godog.DocString) error { return nil })
+	test(t, func(a []byte) error { return nil })
+
+}
+
+func TestStepDefinition_Run_InvalidHandlerParamConversion(t *testing.T) {
+	test := func(t *testing.T, fn interface{}) {
+		def := &models.StepDefinition{
+			StepDefinition: formatters.StepDefinition{
+				Handler: fn,
+			},
+			HandlerValue: reflect.ValueOf(fn),
+		}
+
+		def.Args = []interface{}{12}
+
+		res := def.Run()
+		if res == nil {
+			t.Fatalf("expected an unsupported argument type error, but got none")
+		}
+
+		err, ok := res.(error)
+		if !ok {
+			t.Fatalf("expected an unsupported argument type error, but got %T instead", res)
+		}
+
+		if !errors.Is(err, models.ErrUnsupportedArgumentType) {
+			t.Fatalf("expected an unsupported argument type error, but got '%v' instead", err)
+		}
+	}
+
+	// Lists some unsupported argument types for step handler.
+
+	// Pointers should work only for godog.Table/godog.DocString
+	test(t, func(a *int) error { return nil })
+	test(t, func(a *int64) error { return nil })
+	test(t, func(a *int32) error { return nil })
+	test(t, func(a *int16) error { return nil })
+	test(t, func(a *int8) error { return nil })
+	test(t, func(a *string) error { return nil })
+	test(t, func(a *float64) error { return nil })
+	test(t, func(a *float32) error { return nil })
+
+	// I cannot pass structures
+	test(t, func(a godog.Table) error { return nil })
+	test(t, func(a godog.DocString) error { return nil })
+	test(t, func(a testStruct) error { return nil })
+
+	// I cannot use maps
+	test(t, func(a map[string]interface{}) error { return nil })
+	test(t, func(a map[string]int) error { return nil })
+
+	// Slice works only for byte
+	test(t, func(a []int) error { return nil })
+	test(t, func(a []string) error { return nil })
+	test(t, func(a []bool) error { return nil })
+
+	// I cannot use bool
+	test(t, func(a bool) error { return nil })
+
+}
+
+func TestStepDefinition_Run_StringConversionToFunctionType(t *testing.T) {
+	test := func(t *testing.T, fn interface{}, args []interface{}) {
+		def := &models.StepDefinition{
+			StepDefinition: formatters.StepDefinition{
+				Handler: fn,
+			},
+			HandlerValue: reflect.ValueOf(fn),
+			Args:         args,
+		}
+
+		res := def.Run()
+		if res == nil {
+			t.Fatalf("expected a cannot convert argument type error, but got none")
+		}
+
+		err, ok := res.(error)
+		if !ok {
+			t.Fatalf("expected a cannot convert argument type error, but got %T instead", res)
+		}
+
+		if !errors.Is(err, models.ErrCannotConvert) {
+			t.Fatalf("expected a cannot convert argument type error, but got '%v' instead", err)
+		}
+	}
+
+	// Lists some unsupported argument types for step handler.
+
+	// Cannot convert invalid int
+	test(t, func(a int) error { return nil }, []interface{}{"a"})
+	test(t, func(a int64) error { return nil }, []interface{}{"a"})
+	test(t, func(a int32) error { return nil }, []interface{}{"a"})
+	test(t, func(a int16) error { return nil }, []interface{}{"a"})
+	test(t, func(a int8) error { return nil }, []interface{}{"a"})
+
+	// Cannot convert invalid float
+	test(t, func(a float32) error { return nil }, []interface{}{"a"})
+	test(t, func(a float64) error { return nil }, []interface{}{"a"})
+
+	// Cannot convert to DataArg
+	test(t, func(a *godog.Table) error { return nil }, []interface{}{"194"})
+
+	// Cannot convert to DocString ?
+	test(t, func(a *godog.DocString) error { return nil }, []interface{}{"194"})
+
+}
+
+// @TODO maybe we should support duration
+// fn2 := func(err time.Duration) error { return nil }
+// def = &models.StepDefinition{Handler: fn2, HandlerValue: reflect.ValueOf(fn2)}
+
+// def.Args = []interface{}{"1"}
+// if err := def.Run(); err == nil {
+// 	t.Fatalf("expected an error due to wrong argument type, but got none")
+// }
+
+type testStruct struct {
+	a string
 }

 func TestShouldSupportDocStringToStringConversion(t *testing.T) {
--- a/run_test.go
+++ b/run_test.go
@ -568,7 +568,8 @@ type progressOutput struct {
 	bottomRows      []string
 }

-func passingStepDef() error { return nil }
+func passingStepDef() error        { return nil }
+func passingStepDefWithoutReturn() {}

 func oddEvenStepDef(odd, even int) error { return oddOrEven(odd, even) }

--- a/suite_context_test.go
+++ b/suite_context_test.go
@ -108,6 +108,7 @@ func InitializeScenario(ctx *ScenarioContext) {
 		return nil
 	})

+	ctx.Step(`^(?:a )?passing step without return$`, func() {})
 	ctx.BeforeStep(tc.inject)
 }

@ -424,9 +425,8 @@ func (tc *godogFeaturesScenario) aFeatureFile(path string, body *DocString) erro
 	return err
 }

-func (tc *godogFeaturesScenario) featurePath(path string) error {
+func (tc *godogFeaturesScenario) featurePath(path string) {
 	tc.paths = append(tc.paths, path)
-	return nil
 }

 func (tc *godogFeaturesScenario) parseFeatures() error {
--- a/test_context.go
+++ b/test_context.go
@ -12,6 +12,9 @@ import (
 	"github.com/cucumber/godog/internal/models"
 )

+// matchable errors
+var ()
+
 // Scenario represents the executed scenario
 type Scenario = messages.Pickle

@ -176,8 +179,8 @@ func (ctx *ScenarioContext) Step(expr, stepFunc interface{}) {
 		panic(fmt.Sprintf("expected handler to be func, but got: %T", stepFunc))
 	}

-	if typ.NumOut() != 1 {
-		panic(fmt.Sprintf("expected handler to return only one value, but it has: %d", typ.NumOut()))
+	if typ.NumOut() > 1 {
+		panic(fmt.Sprintf("expected handler to return either zero or one value, but it has: %d", typ.NumOut()))
 	}

 	def := &models.StepDefinition{
@ -188,19 +191,21 @@ func (ctx *ScenarioContext) Step(expr, stepFunc interface{}) {
 		HandlerValue: v,
 	}

-	typ = typ.Out(0)
-	switch typ.Kind() {
-	case reflect.Interface:
-		if !typ.Implements(errorInterface) {
-			panic(fmt.Sprintf("expected handler to return an error, but got: %s", typ.Kind()))
+	if typ.NumOut() == 1 {
+		typ = typ.Out(0)
+		switch typ.Kind() {
+		case reflect.Interface:
+			if !typ.Implements(errorInterface) {
+				panic(fmt.Sprintf("expected handler to return an error, but got: %s", typ.Kind()))
+			}
+		case reflect.Slice:
+			if typ.Elem().Kind() != reflect.String {
+				panic(fmt.Sprintf("expected handler to return []string for multistep, but got: []%s", typ.Elem().Kind()))
+			}
+			def.Nested = true
+		default:
+			panic(fmt.Sprintf("expected handler to return an error or []string, but got: %s", typ.Kind()))
 		}
-	case reflect.Slice:
-		if typ.Elem().Kind() != reflect.String {
-			panic(fmt.Sprintf("expected handler to return []string for multistep, but got: []%s", typ.Kind()))
-		}
-		def.Nested = true
-	default:
-		panic(fmt.Sprintf("expected handler to return an error or []string, but got: %s", typ.Kind()))
 	}

 	ctx.suite.steps = append(ctx.suite.steps, def)
--- a/test_context_test.go
+++ b/test_context_test.go
@ -0,0 +1,67 @@
+package godog
+
+import (
+	"fmt"
+	"regexp"
+	"testing"
+
+	. "github.com/smartystreets/goconvey/convey"
+)
+
+func TestScenarioContext_Step(t *testing.T) {
+	Convey("When adding steps to ScenarioContext ", t, func() {
+		ctx := ScenarioContext{suite: &suite{}}
+
+		Convey("It should accept steps defined with regexp.Regexp", func() {
+			re := regexp.MustCompile(`(?:it is a test)?.{10}x*`)
+			So(func() { ctx.Step(re, okEmptyResult) }, ShouldNotPanic)
+		})
+
+		Convey("It should accept steps defined with bytes slice", func() {
+			So(func() { ctx.Step([]byte("(?:it is a test)?.{10}x*"), okEmptyResult) }, ShouldNotPanic)
+		})
+
+		Convey("It should accept steps handler with empty return", func() {
+			So(func() { ctx.Step(".*", okEmptyResult) }, ShouldNotPanic)
+		})
+
+		Convey("It should accept steps handler with error return", func() {
+			So(func() { ctx.Step(".*", okErrorResult) }, ShouldNotPanic)
+		})
+
+		Convey("It should accept steps handler with string slice return", func() {
+			So(func() { ctx.Step(".*", okSliceResult) }, ShouldNotPanic)
+		})
+
+		Convey("It should panic if step expression is neither a string, regex or byte slice", func() {
+			So(func() { ctx.Step(1251, okSliceResult) }, ShouldPanicWith, fmt.Sprintf("expecting expr to be a *regexp.Regexp or a string, got type: %T", 12))
+		})
+		Convey("It should panic if step handler", func() {
+			Convey("is not a function", func() {
+				So(func() { ctx.Step(".*", 124) }, ShouldPanicWith, fmt.Sprintf("expected handler to be func, but got: %T", 12))
+			})
+
+			Convey("has more than 1 return value", func() {
+				So(func() { ctx.Step(".*", nokLimitCase) }, ShouldPanicWith, fmt.Sprintf("expected handler to return either zero or one value, but it has: 2"))
+				So(func() { ctx.Step(".*", nokMore) }, ShouldPanicWith, fmt.Sprintf("expected handler to return either zero or one value, but it has: 5"))
+			})
+
+			Convey("return type is not an error or string slice or void", func() {
+				So(func() { ctx.Step(".*", nokInvalidReturnInterfaceType) }, ShouldPanicWith, "expected handler to return an error, but got: interface")
+				So(func() { ctx.Step(".*", nokInvalidReturnSliceType) }, ShouldPanicWith, "expected handler to return []string for multistep, but got: []int")
+				So(func() { ctx.Step(".*", nokInvalidReturnOtherType) }, ShouldPanicWith, "expected handler to return an error or []string, but got: chan")
+			})
+		})
+
+	})
+
+}
+
+func okEmptyResult()                             {}
+func okErrorResult() error                       { return nil }
+func okSliceResult() []string                    { return nil }
+func nokLimitCase() (int, error)                 { return 0, nil }
+func nokMore() (int, int, int, int, error)       { return 0, 0, 0, 0, nil }
+func nokInvalidReturnInterfaceType() interface{} { return 0 }
+func nokInvalidReturnSliceType() []int           { return nil }
+func nokInvalidReturnOtherType() chan int        { return nil }