diff --git a/fmt_progress_test.go b/fmt_progress_test.go
index 5b48b97..eb32f48 100644
--- a/fmt_progress_test.go
+++ b/fmt_progress_test.go
@@ -20,19 +20,20 @@ func TestProgressFormatterOutput(t *testing.T) {
 
 	var buf bytes.Buffer
 	w := colors.Uncolored(&buf)
-	s := &Suite{
+	r := runner{
 		fmt: progressFunc("progress", w),
 		features: []*feature{&feature{
 			Path:    "any.feature",
 			Feature: feat,
 			Content: []byte(sampleGherkinFeature),
 		}},
+		initializer: func(s *Suite) {
+			s.Step(`^passing$`, func() error { return nil })
+			s.Step(`^failing$`, func() error { return fmt.Errorf("errored") })
+			s.Step(`^pending$`, func() error { return ErrPending })
+		},
 	}
 
-	s.Step(`^passing$`, func() error { return nil })
-	s.Step(`^failing$`, func() error { return fmt.Errorf("errored") })
-	s.Step(`^pending$`, func() error { return ErrPending })
-
 	// var zeroDuration time.Duration
 	expected := `
 ...F-.P-.UU.....F..P..U 23
@@ -72,8 +73,7 @@ func FeatureContext(s *godog.Suite) {
 	expected = fmt.Sprintf(expected, zeroDuration.String(), os.Getenv("GODOG_SEED"))
 	expected = trimAllLines(expected)
 
-	s.run()
-	s.fmt.Summary()
+	r.run()
 
 	actual := trimAllLines(buf.String())
 	if actual != expected {
diff --git a/stepdef_test.go b/stepdef_test.go
new file mode 100644
index 0000000..59ab016
--- /dev/null
+++ b/stepdef_test.go
@@ -0,0 +1,106 @@
+package godog
+
+import (
+	"reflect"
+	"strings"
+	"testing"
+
+	"github.com/DATA-DOG/godog/gherkin"
+)
+
+func TestShouldSupportIntTypes(t *testing.T) {
+	fn := func(a int64, b int32, c int16, d int8) error { return nil }
+
+	def := &StepDef{
+		Handler: fn,
+		hv:      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 TestShouldSupportFloatTypes(t *testing.T) {
+	fn := func(a float64, b float32) error { return nil }
+
+	def := &StepDef{
+		Handler: fn,
+		hv:      reflect.ValueOf(fn),
+	}
+
+	def.args = []interface{}{"1.1", "1.09"}
+	if err := def.run(); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	def.args = []interface{}{"1.08", strings.Repeat("1", 65) + ".67"}
+	if err := def.run(); err == nil {
+		t.Fatalf("expected convertion fail for float32, but got none")
+	}
+}
+
+func TestShouldNotSupportOtherPointerTypesThanGherkin(t *testing.T) {
+	fn1 := func(a *int) error { return nil }
+	fn2 := func(a *gherkin.DocString) error { return nil }
+	fn3 := func(a *gherkin.DataTable) error { return nil }
+
+	def1 := &StepDef{Handler: fn1, hv: reflect.ValueOf(fn1), args: []interface{}{(*int)(nil)}}
+	def2 := &StepDef{Handler: fn2, hv: reflect.ValueOf(fn2), args: []interface{}{(*gherkin.DocString)(nil)}}
+	def3 := &StepDef{Handler: fn3, hv: reflect.ValueOf(fn3), args: []interface{}{(*gherkin.DataTable)(nil)}}
+
+	if err := def1.run(); err == nil {
+		t.Fatalf("expected conversion error, but got none")
+	}
+	if err := def2.run(); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if err := def3.run(); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+}
+
+func TestShouldSupportOnlyByteSlice(t *testing.T) {
+	fn1 := func(a []byte) error { return nil }
+	fn2 := func(a []string) error { return nil }
+
+	def1 := &StepDef{Handler: fn1, hv: reflect.ValueOf(fn1), args: []interface{}{"str"}}
+	def2 := &StepDef{Handler: fn2, hv: reflect.ValueOf(fn2), args: []interface{}{[]string{}}}
+
+	if err := def1.run(); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if err := def2.run(); err == nil {
+		t.Fatalf("expected conversion error, but got none")
+	}
+}
+
+func TestUnexpectedArguments(t *testing.T) {
+	fn := func(a, b int) error { return nil }
+	def := &StepDef{Handler: fn, hv: reflect.ValueOf(fn)}
+
+	def.args = []interface{}{"1"}
+	if err := def.run(); err == 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")
+	}
+
+	// @TODO maybe we should support duration
+	// fn2 := func(err time.Duration) error { return nil }
+	// def = &StepDef{Handler: fn2, hv: 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")
+	// }
+}