diff --git a/core/adapter/adapter.go b/core/adapter/event.go
similarity index 100%
rename from core/adapter/adapter.go
rename to core/adapter/event.go
diff --git a/core/adapter/experiment.go b/core/adapter/experiment.go
new file mode 100644
index 0000000..999387b
--- /dev/null
+++ b/core/adapter/experiment.go
@@ -0,0 +1,23 @@
+package adapter
+
+import (
+	"fmt"
+
+	"Growth/core/entity"
+)
+
+type ExperimentStore interface {
+	Save(entity.Experiment) entity.Experiment
+	FetchByID(id entity.ID) entity.Experiment
+	ErrNotFound() *ErrExperimentNotFound
+	ErrOther() error
+}
+
+type ErrExperimentNotFound struct {
+	ID    entity.ID
+	Stack string
+}
+
+func (e *ErrExperimentNotFound) Error() string {
+	return fmt.Sprintf("experiment:%d not found", e.ID)
+}
diff --git a/core/adapter/testadapter/test_adapter.go b/core/adapter/testadapter/test_event.go
similarity index 100%
rename from core/adapter/testadapter/test_adapter.go
rename to core/adapter/testadapter/test_event.go
diff --git a/core/adapter/testadapter/test_experiment.go b/core/adapter/testadapter/test_experiment.go
new file mode 100644
index 0000000..80a2881
--- /dev/null
+++ b/core/adapter/testadapter/test_experiment.go
@@ -0,0 +1,61 @@
+package testadapter
+
+import (
+	"runtime/debug"
+
+	"Growth/core/adapter"
+	"Growth/core/entity"
+)
+
+type FakeExperimentStore struct {
+	experiments []entity.Experiment
+	errNotFound *adapter.ErrExperimentNotFound
+	errOther    error
+}
+
+func (store *FakeExperimentStore) Save(e entity.Experiment) entity.Experiment {
+	store.init()
+	e.ID = entity.ID(len(store.experiments) + 1)
+	store.experiments = append(store.experiments, e)
+	return e
+}
+
+func (store *FakeExperimentStore) FetchByID(id entity.ID) entity.Experiment {
+	for _, e := range store.experiments {
+		if e.ID == id {
+			return e
+		}
+	}
+	store.errNotFound =&adapter.ErrExperimentNotFound{ID: id, Stack: string(debug.Stack())}
+	return entity.Experiment{}
+}
+
+func (store *FakeExperimentStore) ErrNotFound() *adapter.ErrExperimentNotFound {
+	defer func() {
+		store.errNotFound = nil
+	}()
+	return store.errNotFound
+}
+
+func (store *FakeExperimentStore) ErrNotFoundTrace() *adapter.ErrExperimentNotFound {
+	defer func() {
+		store.errNotFound = nil
+	}()
+	return store.errNotFound
+}
+
+func (store *FakeExperimentStore) ErrOther() error {
+	defer func() {
+		store.errOther = nil
+	}()
+	return store.errOther
+}
+
+func (store *FakeExperimentStore) init() {
+	if store == nil {
+		*store = FakeExperimentStore{}
+	}
+	if store.experiments == nil {
+		store.experiments = make([]entity.Experiment, 0)
+	}
+}
diff --git a/core/usecase/evenet_test.go b/core/usecase/evenet_test.go
new file mode 100644
index 0000000..84eece5
--- /dev/null
+++ b/core/usecase/evenet_test.go
@@ -0,0 +1,86 @@
+package usecase
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+type EventType int
+
+type Event struct {
+	Type EventType
+	Data interface{}
+}
+
+type EventBus struct {
+	qs map[EventType][]chan Out
+}
+
+func (bus *EventBus) init() {
+	if bus.qs == nil {
+		bus.qs = make(map[EventType][]chan Out)
+	}
+}
+
+func (bus *EventBus) Emit(e Event) error {
+	bus.init()
+	for _, out := range bus.qs[e.Type] {
+		go func(out chan Out) {
+			out <- Out{
+				Data: e.Data,
+				Error: nil,
+			}
+		}(out)
+	}
+	return nil
+}
+
+type Out struct {
+	Data interface{}
+	Error error
+}
+
+func (bus *EventBus) On(et EventType) chan Out {
+	bus.init()
+	// register a queue for this listener
+	outs := bus.qs[et]
+	out := make(chan Out)
+	bus.qs[et] = append(outs, out)
+	return out
+}
+
+const (
+	EventX EventType = iota
+	EventY
+	EventZ
+)
+
+func TestX(t *testing.T) {
+	defer func() {
+		recover()
+	}()
+
+	bus := &EventBus{}
+
+	xChan := bus.On(EventX)
+	xChan2 := bus.On(EventX)
+
+	bus.Emit(Event{
+		Type: EventType(EventX),
+		Data: "1",
+	})
+	bus.Emit(Event{
+		Type: EventType(EventX),
+		Data: "1",
+	})
+
+	out := <-xChan
+	require.Equal(t, "1", out.Data)
+	require.Equal(t, nil, out.Error)
+
+	out = <-xChan2
+	require.Equal(t, "1", out.Data)
+	require.Equal(t, nil, out.Error)
+
+}
diff --git a/core/usecase/event_test.go b/core/usecase/event_test.go
index a089588..c8d6f19 100644
--- a/core/usecase/event_test.go
+++ b/core/usecase/event_test.go
@@ -21,7 +21,7 @@ func TestFetchEventById(t *testing.T) {
 
 	t.Run("event not found when store is empty", func(t *testing.T) {
 		e, err := FetchEventByID(1, eventStore)
-		require.IsType(t, &adapter.ErrEventNotFound{}, err)
+		require.IsType(t, &adapter.ErrEventNotFound{}, err) // todo: an error leak here, should define use case level error for it
 		require.Equal(t, "event:1 not found", err.Error())
 		require.Equal(t, entity.Event{}, e)
 	})
diff --git a/core/usecase/experiment.go b/core/usecase/experiment.go
index 3d31d85..c20357e 100644
--- a/core/usecase/experiment.go
+++ b/core/usecase/experiment.go
@@ -1,7 +1,43 @@
 package usecase
 
-import "Growth/core/entity"
+import (
+	"Growth/core/adapter"
+	"Growth/core/entity"
+)
 
-func CreateExperiment(userID entity.ID) (entity.Experiment, error) {
-	return entity.Experiment{Owner: userID}, nil
+func NewExperiment(store adapter.ExperimentStore) *Experiment {
+	return &Experiment{store: store}
+}
+
+type Experiment struct {
+	store                 adapter.ExperimentStore
+	errExperimentNotFound *adapter.ErrExperimentNotFound
+	errOther              error
+}
+
+func (e *Experiment) CreateExperiment(userID entity.ID) (entity.Experiment) {
+	exp := e.store.Save(entity.Experiment{Owner: userID})
+	e.errOther = e.store.ErrOther()
+	return exp
+}
+
+func (e *Experiment) FetchExperimentByID(id entity.ID) entity.Experiment {
+	exp := e.store.FetchByID(id)
+	e.errExperimentNotFound = e.store.ErrNotFound()
+	e.errOther = e.store.ErrOther()
+	return exp
+}
+
+func (e *Experiment) ErrExperimentNotFound() *adapter.ErrExperimentNotFound {
+	defer func() {
+		e.errExperimentNotFound = nil
+	}()
+	return e.errExperimentNotFound
+}
+
+func (e *Experiment) ErrOther() error {
+	defer func() {
+		e.errOther = nil
+	}()
+	return e.errOther
 }
diff --git a/core/usecase/experiment_test.go b/core/usecase/experiment_test.go
index 84ba6e9..96afc8d 100644
--- a/core/usecase/experiment_test.go
+++ b/core/usecase/experiment_test.go
@@ -5,19 +5,34 @@ import (
 	"testing"
 	"time"
 
+	"Growth/core/adapter/testadapter"
 	"Growth/core/entity"
 
 	"github.com/stretchr/testify/require"
 )
 
-func TestCreateExperiment(t *testing.T) {
-	t.Run("the owner of an experiment is correctly set", func(t *testing.T) {
+func TestExperiment(t *testing.T) {
+	e := NewExperiment(&testadapter.FakeExperimentStore{})
+
+	t.Run("no data when the store is empty", func(t *testing.T) {
+		e.FetchExperimentByID(entity.ID(1))
+		require.Equal(t, entity.ID(1), e.ErrExperimentNotFound().ID)
+	})
+
+	t.Run("can find the same experiment which has been created", func(t *testing.T) {
 		rand.Seed(time.Now().Unix())
 		for i := 0; i < 10; i++ {
-			id := entity.ID(rand.Int63())
-			exp, err := CreateExperiment(id)
-			require.NoError(t, err)
-			require.Equal(t, id, exp.Owner)
+			userID := entity.ID(rand.Int63())
+			exp := e.CreateExperiment(userID)
+			require.NoError(t, e.ErrOther())
+			require.Equal(t, userID, exp.Owner)
+
+			exp2 := e.FetchExperimentByID(exp.ID)
+			require.Nil(t, e.ErrExperimentNotFound())
+			require.NoError(t, e.ErrOther())
+
+			require.Equal(t, exp2.ID, exp.ID, entity.ID(i+1))
+			require.Equal(t, userID, exp2.Owner)
 		}
 	})
 }
diff --git a/dep/dep.go b/dep/dep.go
index 0bf198b..a5495f5 100644
--- a/dep/dep.go
+++ b/dep/dep.go
@@ -31,6 +31,7 @@ func (d *Dep) RelayHandler() http.Handler {
 			EventStore: d.EventStore,
 		},
 	}
+
 	h, err := server.RelayHandler(schema, r)
 	d.Err = errors.WithStack(err)
 	return h