fix: return an error when no matching flow is found when running regi…

…stry

registry/registry.go

@@ -2,6 +2,8 @@ package registry
 
 import (
 	"context"
+	"errors"
+	"fmt"
 
 	"github.com/hiroara/carbo/flow"
 )
@@ -20,9 +22,16 @@ func New() *Registry {
 	return &Registry{factories: make(map[string]flow.Factory)}
 }
 
+var ErrNoMatchingFlow = errors.New("no matching flow is found")
+
 // Build a registered Flow selected with the passed name, and run it.
 func (r *Registry) Run(ctx context.Context, name string) error {
-	f, err := r.factories[name].Build()
+	fac, ok := r.factories[name]
+	if !ok {
+		return fmt.Errorf("%w with name \"%s\"", ErrNoMatchingFlow, name)
+	}
+
+	f, err := fac.Build()
 	if err != nil {
 		return err
 	}

registry/registry_test.go

@@ -17,24 +17,34 @@ import (
 func TestRegistryRun(t *testing.T) {
 	t.Parallel()
 
-	r := registry.New()
+	t.Run("NormalCase", func(t *testing.T) {
+		t.Parallel()
 
-	src := source.FromSlice([]string{"item1", "item2"})
+		r := registry.New()
 
-	out := make([]string, 0)
-	sink := sink.ToSlice(&out)
-	conn := task.Connect(src.AsTask(), sink.AsTask(), 2)
-	called := false
+		src := source.FromSlice([]string{"item1", "item2"})
+		out := make([]string, 0)
+		sink := sink.ToSlice(&out)
+		conn := task.Connect(src.AsTask(), sink.AsTask(), 2)
+		called := false
 
-	r.Register("flow1", flow.NewFactory(func() (*flow.Flow, error) {
-		called = true
-		return flow.FromTask(conn), nil
-	}))
+		r.Register("flow1", flow.NewFactory(func() (*flow.Flow, error) {
+			called = true
+			return flow.FromTask(conn), nil
+		}))
 
-	err := r.Run(context.Background(), "flow1")
-	require.NoError(t, err)
+		err := r.Run(context.Background(), "flow1")
+		require.NoError(t, err)
 
-	if assert.True(t, called) {
-		assert.Equal(t, []string{"item1", "item2"}, out)
-	}
+		if assert.True(t, called) {
+			assert.Equal(t, []string{"item1", "item2"}, out)
+		}
+	})
+
+	t.Run("NoMatchingFlowCase", func(t *testing.T) {
+		t.Parallel()
+
+		r := registry.New()
+		assert.ErrorIs(t, r.Run(context.Background(), "unknown"), registry.ErrNoMatchingFlow)
+	})
 }