diff --git a/test_fsf/main.go b/test_fsf/main.go
new file mode 100644
index 0000000000..4d45a168d0
--- /dev/null
+++ b/test_fsf/main.go
@@ -0,0 +1,69 @@
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"log"
+
+	"google.golang.org/api/ondemandscanning/v1"
+)
+
+func expect(title string, x any, result string) {
+	b, err := json.Marshal(x)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	bb := string(b)
+	if bb == result {
+		fmt.Printf("OK %s %q\n", title, bb)
+	} else {
+		fmt.Printf("ERR %s Expected %q, got %q\n", title, result, bb)
+	}
+}
+
+func main() {
+	expect("Empty slice, no FSF", &ondemandscanning.GrafeasV1LayerDetails{
+		BaseImages: []*ondemandscanning.GrafeasV1BaseImage{},
+	}, "{}")
+
+	expect("Empty slice, empty FSF", &ondemandscanning.GrafeasV1LayerDetails{
+		BaseImages:      []*ondemandscanning.GrafeasV1BaseImage{},
+		ForceSendFields: []string{""},
+	}, "{}")
+
+	expect("Empty slice + FSF", &ondemandscanning.GrafeasV1LayerDetails{
+		BaseImages:      []*ondemandscanning.GrafeasV1BaseImage{},
+		ForceSendFields: []string{"BaseImages"},
+	}, `{"baseImages":[]}`)
+
+	expect("non-empty slice + FSF", &ondemandscanning.GrafeasV1LayerDetails{
+		BaseImages:      []*ondemandscanning.GrafeasV1BaseImage{{LayerCount: 25}},
+		ForceSendFields: []string{"BaseImages"},
+	}, `{"baseImages":[{"layerCount":25}]}`)
+
+	expect("nil slice + FSF", &ondemandscanning.GrafeasV1LayerDetails{
+		// BaseImages:      nil,
+		ForceSendFields: []string{"BaseImages"},
+	}, `{"baseImages":[]}`) // this is unexpected
+
+	expect("nil slice + NullFields", &ondemandscanning.GrafeasV1LayerDetails{
+		BaseImages: nil,
+		NullFields: []string{"BaseImages"},
+	}, `{"baseImages":null}`)
+
+	expect("nil slice + FSF + NullFields", &ondemandscanning.GrafeasV1LayerDetails{
+		BaseImages:      nil,
+		ForceSendFields: []string{"BaseImages"},
+		NullFields:      []string{"BaseImages"},
+	}, `{"baseImages":null}`) // NullFields wins
+
+	expect("Empty map, no FSF", &ondemandscanning.GrafeasV1SlsaProvenanceZeroTwoSlsaConfigSource{
+		Digest: map[string]string{},
+	}, "{}")
+
+	expect("Empty map + FSF", &ondemandscanning.GrafeasV1SlsaProvenanceZeroTwoSlsaConfigSource{
+		Digest:          map[string]string{},
+		ForceSendFields: []string{"Digest"},
+	}, `{"digest":{}}`)
+}