diff --git a/go.mod b/go.mod
index be8d218..f90955c 100644
--- a/go.mod
+++ b/go.mod
@@ -1,3 +1,10 @@
 module gitea.rosskeen.house/rosskeen.house/machine
 
 go 1.21.1
+
+require (
+	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/pmezard/go-difflib v1.0.0 // indirect
+	github.com/stretchr/testify v1.9.0 // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
+)
diff --git a/go.sum b/go.sum
new file mode 100644
index 0000000..e20fa14
--- /dev/null
+++ b/go.sum
@@ -0,0 +1,9 @@
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/testify v1.9.0 h1:HtqpIVDClZ4nwg75+f6Lvsy/wHu+3BoSGCbBAcpTsTg=
+github.com/stretchr/testify v1.9.0/go.mod h1:r2ic/lqez/lEtzL7wO/rwa5dbSLXVDPFyf8C91i36aY=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
diff --git a/machine.go b/machine.go
index f187a84..fa05c97 100644
--- a/machine.go
+++ b/machine.go
@@ -14,7 +14,7 @@ type Stater interface {
   AddTransition(trigger string, source State, dest State)
   AddSubscription(transition string, subscription Subscriber) error
   AddModel(m Modeler)
-  Trigger(transition string)
+  Trigger(transition string) error
   CurrentState() State
 }
 
@@ -50,8 +50,8 @@ func (d *Definition) AddModel(m Modeler) {
   d.model = m
 }
 
-func (d *Definition) Trigger(transition string) {
-  d.triggers[transition].Run(d.model)
+func (d *Definition) Trigger(transition string) error {
+  return d.triggers[transition].Run(d.model)
 }
 
 func (d *Definition) CurrentState() State {
@@ -61,6 +61,7 @@ func (d *Definition) CurrentState() State {
 func (d *Definition) AddSubscription(transition string, subscription Subscriber) error {
   if t,ok := d.triggers[transition]; ok {
     t.Subscribe(subscription)
+		return nil
   }
   return errors.New("Transition does not exist")
 }
diff --git a/machine_test.go b/machine_test.go
index cd8f1c0..821faa9 100644
--- a/machine_test.go
+++ b/machine_test.go
@@ -5,6 +5,7 @@ package machine
 import(
   "log"
   "testing"
+	"github.com/stretchr/testify/assert"
 )
 
 func setupStater(initial State) Stater {
@@ -41,7 +42,8 @@ func TestMachineAddTransition(t *testing.T) {
   s.AddTransition("connect", "disconnected", "start_connection")
   s.AddModel(setupModel("disconnected"))
   // worker gets a trigger message
-  s.Trigger("connect")
+  assert.Nil(t, s.Trigger("connect"))
+	
   // machine generates transition event mesages
   if s.CurrentState() != "start_connection" {
     t.Errorf("State transition failed for: connect - %s", s.CurrentState())
@@ -53,7 +55,7 @@ func TestMachineAddSubscription(t *testing.T) {
   s := setupStater("disconnected")
   s.AddStates("disconnected", "start_connection", "connected")
   s.AddTransition("connect", "disconnected", "start_connection")
-  s.AddSubscription("connect", x)
+  assert.Nil(t, s.AddSubscription("connect", x))
   s.AddModel(setupModel("disconnected"))
   s.Trigger("connect")
   exitMessage := <- *x.(*EventChannel)
diff --git a/model.go b/model.go
index 2ac49fa..00176cb 100644
--- a/model.go
+++ b/model.go
@@ -3,7 +3,7 @@
 package machine
 
 type Modeler interface {
-  Trigger(transition Transitioner)
+  Trigger(transition Transitioner) error
   ChangeState(target State) State
   InspectState() State
 }
@@ -16,8 +16,8 @@ func NewModel(initial State) Modeler {
   return &Model{ state: initial }
 }
 
-func (m *Model) Trigger(transition Transitioner) {
-  transition.Run(m)
+func (m *Model) Trigger(transition Transitioner) error {
+  return transition.Run(m)
 }
 
 func (m *Model) ChangeState(target State) State {
diff --git a/transition_test.go b/transition_test.go
index 0f57b92..015e4a2 100644
--- a/transition_test.go
+++ b/transition_test.go
@@ -5,6 +5,7 @@ package machine
 import (
   "log"
   "testing"
+	"github.com/stretchr/testify/assert"
 )
 
 func setupTransition() Transitioner {
@@ -30,7 +31,7 @@ func TestNewTransition(t *testing.T) {
 func TestTransitionExecution(t *testing.T) {
   s := setupTransition()
   m := setupModel("closed")
-  s.Run(m)
+  assert.Nil(t, s.Run(m))
   state := m.InspectState()
   if state != "open" {
     t.Errorf("Failed to transition state: %s", state)
@@ -42,7 +43,7 @@ func TestTransitionSubscribe(t *testing.T) {
   s := setupTransition()
   s.Subscribe(c)
   m := setupModel("closed")
-  s.Run(m)
+  assert.Nil(t, s.Run(m))
   exitEvent := <- *c.(*EventChannel)
   enterEvent := <- *c.(*EventChannel)
   if exitEvent.on != EXITSTATEEVENT {