add ftltest support for Next()

backend/controller/dal/testdata/go/fsmnext/fsmnext_test.go

@@ -0,0 +1,36 @@
+package fsmnext
+
+import (
+	"testing"
+
+	"github.com/TBD54566975/ftl/go-runtime/ftl"
+	"github.com/TBD54566975/ftl/go-runtime/ftl/ftltest"
+	"github.com/alecthomas/assert/v2"
+)
+
+func TestProgression(t *testing.T) {
+	// Simple progression through each state
+	ctx := ftltest.Context()
+
+	assert.NoError(t, SendOne(ctx, Request{
+		State: A,
+		Event: Event{
+			Instance:   "1",
+			NextStates: []State{B, C, D},
+		},
+	}))
+}
+
+func TestDoubleNext(t *testing.T) {
+	// Bad progression where fsm.Next() is called twice
+	ctx := ftltest.Context()
+
+	assert.Contains(t, SendOne(ctx, Request{
+		State: A,
+		Event: Event{
+			Instance:     "1",
+			NextStates:   []State{B},
+			NextAttempts: ftl.Some(2),
+		},
+	}).Error(), `fsm "fsm" instance "1" already has a pending event`)
+}

backend/controller/dal/testdata/go/fsmnext/go.mod

@@ -2,45 +2,62 @@ module ftl/fsmnext
 
 go 1.22.5
 
-require github.com/TBD54566975/ftl v1.1.5
+require (
+	github.com/TBD54566975/ftl v1.1.5
+	github.com/alecthomas/assert/v2 v2.10.0
+)
 
 require (
 	connectrpc.com/connect v1.16.2 // indirect
 	connectrpc.com/grpcreflect v1.2.0 // indirect
 	connectrpc.com/otelconnect v0.7.1 // indirect
+	github.com/BurntSushi/toml v1.4.0 // indirect
+	github.com/TBD54566975/scaffolder v1.0.0 // indirect
 	github.com/alecthomas/atomic v0.1.0-alpha2 // indirect
 	github.com/alecthomas/concurrency v0.0.2 // indirect
 	github.com/alecthomas/participle/v2 v2.1.1 // indirect
+	github.com/alecthomas/repr v0.4.0 // indirect
 	github.com/alecthomas/types v0.16.0 // indirect
 	github.com/alessio/shellescape v1.4.2 // indirect
+	github.com/amacneil/dbmate/v2 v2.19.0 // indirect
+	github.com/aws/aws-sdk-go-v2 v1.30.3 // indirect
+	github.com/aws/aws-sdk-go-v2/internal/configsources v1.3.15 // indirect
+	github.com/aws/aws-sdk-go-v2/internal/endpoints/v2 v2.6.15 // indirect
+	github.com/aws/aws-sdk-go-v2/service/secretsmanager v1.32.4 // indirect
+	github.com/aws/smithy-go v1.20.3 // indirect
 	github.com/benbjohnson/clock v1.3.5 // indirect
 	github.com/danieljoos/wincred v1.2.0 // indirect
 	github.com/go-logr/logr v1.4.2 // indirect
 	github.com/go-logr/stdr v1.2.2 // indirect
 	github.com/godbus/dbus/v5 v5.1.0 // indirect
+	github.com/google/uuid v1.6.0 // indirect
 	github.com/hashicorp/cronexpr v1.1.2 // indirect
+	github.com/hexops/gotextdiff v1.0.3 // indirect
+	github.com/jackc/pgerrcode v0.0.0-20240316143900-6e2875d9b438 // indirect
 	github.com/jackc/pgpassfile v1.0.0 // indirect
 	github.com/jackc/pgservicefile v0.0.0-20221227161230-091c0ba34f0a // indirect
 	github.com/jackc/pgx/v5 v5.6.0 // indirect
 	github.com/jackc/puddle/v2 v2.2.1 // indirect
 	github.com/jpillora/backoff v1.0.0 // indirect
 	github.com/kballard/go-shellquote v0.0.0-20180428030007-95032a82bc51 // indirect
+	github.com/lib/pq v1.10.9 // indirect
 	github.com/mattn/go-isatty v0.0.20 // indirect
 	github.com/multiformats/go-base36 v0.2.0 // indirect
 	github.com/puzpuzpuz/xsync/v3 v3.4.0 // indirect
+	github.com/sqlc-dev/pqtype v0.3.0 // indirect
 	github.com/swaggest/jsonschema-go v0.3.72 // indirect
 	github.com/swaggest/refl v1.3.0 // indirect
 	github.com/zalando/go-keyring v0.2.5 // indirect
 	go.opentelemetry.io/otel v1.28.0 // indirect
 	go.opentelemetry.io/otel/metric v1.28.0 // indirect
 	go.opentelemetry.io/otel/trace v1.28.0 // indirect
-	golang.org/x/crypto v0.25.0 // indirect
+	golang.org/x/crypto v0.26.0 // indirect
 	golang.org/x/exp v0.0.0-20240707233637-46b078467d37 // indirect
-	golang.org/x/mod v0.19.0 // indirect
-	golang.org/x/net v0.27.0 // indirect
-	golang.org/x/sync v0.7.0 // indirect
-	golang.org/x/sys v0.22.0 // indirect
-	golang.org/x/text v0.16.0 // indirect
+	golang.org/x/mod v0.20.0 // indirect
+	golang.org/x/net v0.28.0 // indirect
+	golang.org/x/sync v0.8.0 // indirect
+	golang.org/x/sys v0.24.0 // indirect
+	golang.org/x/text v0.17.0 // indirect
 	google.golang.org/protobuf v1.34.2 // indirect
 )
 

go-runtime/ftl/ftltest/fsm.go

@@ -5,13 +5,15 @@ import (
 	"fmt"
 	"reflect"
 
+	"github.com/TBD54566975/ftl/go-runtime/ftl"
 	"github.com/TBD54566975/ftl/go-runtime/ftl/reflection"
 )
 
 type fakeFSMInstance struct {
 	name       string
 	terminated bool
 	state      reflect.Value
+	next       ftl.Option[any]
 }
 
 func newFakeFSMManager() *fakeFSMManager {
@@ -66,14 +68,17 @@ func (f *fakeFSMManager) SendEvent(ctx context.Context, fsm string, instance str
 	}
 
 	out := transition.To.Call([]reflect.Value{reflect.ValueOf(ctx), reflect.ValueOf(event)})
-	var err error
 	erri := out[0]
-	if erri.IsNil() {
-		fsmInstance.state = transition.To
-	} else {
-		err = erri.Interface().(error) //nolint:forcetypeassert
+	if !erri.IsNil() {
+		err := erri.Interface().(error) //nolint:forcetypeassert
 		fsmInstance.state = reflect.Value{}
+		fsmInstance.next = ftl.None[any]()
+		fsmInstance.terminated = true
+		return err
 	}
+
+	fsmInstance.state = transition.To
+
 	currentStateRef := reflection.FuncRef(fsmInstance.state.Interface()).ToSchema()
 
 	// Flag the FSM instance as terminated if the current state is a terminal state.
@@ -83,9 +88,26 @@ func (f *fakeFSMManager) SendEvent(ctx context.Context, fsm string, instance str
 			break
 		}
 	}
-	return err
+
+	if next, ok := fsmInstance.next.Get(); ok {
+		fsmInstance.next = ftl.None[any]()
+		return f.SendEvent(ctx, fsm, instance, next)
+	}
+	return nil
 }
 
 func (f *fakeFSMManager) SetNextFSMEvent(ctx context.Context, fsm string, instance string, event any) error {
-	panic("implement me")
+	key := fsmInstanceKey{fsm, instance}
+	fsmInstance, ok := f.instances[key]
+	if !ok {
+		return fmt.Errorf("fsm %q instance %q not found", fsm, instance)
+	}
+	if fsmInstance.terminated {
+		return fmt.Errorf("fsm %q instance %q is terminated", fsm, instance)
+	}
+	if _, ok := fsmInstance.next.Get(); ok {
+		return fmt.Errorf("fsm %q instance %q already has a pending event", fsm, instance)
+	}
+	fsmInstance.next = ftl.Some(event)
+	return nil
 }