diff --git a/hems/fnn/fnn.go b/hems/fnn/fnn.go
index 35c15f75c..c58b88c48 100644
--- a/hems/fnn/fnn.go
+++ b/hems/fnn/fnn.go
@@ -58,16 +58,19 @@ func NewFromConfig(ctx context.Context, other map[string]any, site site.API) (*F
 		return nil, err
 	}
 
-	maxDimPower := math.Abs(cc.MaxDimPower)
-	if w4G != nil && maxDimPower == 0 {
-		return nil, errors.New("cannot have w4 without power limit")
-	}
-
 	maxCurtailPower := math.Abs(cc.MaxCurtailPower)
 	if cc.MaxPower > 0 {
 		maxCurtailPower = cc.MaxPower
 	}
 
+	return NewFnn(site, math.Abs(cc.MaxDimPower), maxCurtailPower, w3G, s1G, s2G, w4G, cc.Interval)
+}
+
+func NewFnn(site site.API, maxDimPower, maxCurtailPower float64, w3G, s1G, s2G, w4G func() (bool, error), interval time.Duration) (*Fnn, error) {
+	if w4G != nil && maxDimPower == 0 {
+		return nil, errors.New("cannot have w4 without power limit")
+	}
+
 	return &Fnn{
 		log:             util.NewLogger("fnn"),
 		site:            site,
@@ -77,7 +80,7 @@ func NewFromConfig(ctx context.Context, other map[string]any, site site.API) (*F
 		s2:              s2G,
 		w3:              w3G,
 		w4:              w4G,
-		interval:        cc.Interval,
+		interval:        interval,
 	}, nil
 }
 
diff --git a/hems/fnn/fnn_test.go b/hems/fnn/fnn_test.go
new file mode 100644
index 000000000..7a835291a
--- /dev/null
+++ b/hems/fnn/fnn_test.go
@@ -0,0 +1,18 @@
+package fnn
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestFnn(t *testing.T) {
+	// TODO add site
+	fnn, err := NewFnn(nil, 1e3, 1e3, nil, nil, nil, func() (bool, error) {
+		return true, nil
+	}, 0)
+	require.NoError(t, err)
+	require.Nil(t, fnn.Curtailed())
+	// require.NoError(t, fnn.runDim())
+	// require.Equal(t, new(true), fnn.Dimmed())
+}