test(spec): pin the unknown-key diagnostic to one text

The two runtimes each claimed to raise the other's message and nothing
checked it. Both now render the committed text for the committed key.

internal/hierarchy/selector_keys_test.go

@@ -8,26 +8,33 @@ import (
 	"testing"
 )
 
+// selectorKeysGolden is the cross-runtime contract for object selectors: the
+// keys both runtimes accept, and the diagnostic both raise for a key neither
+// can match.
+type selectorKeysGolden struct {
+	Keys              []string `json:"keys"`
+	UnknownKeyExample []string `json:"unknownKeyExample"`
+	UnknownKeyMessage string   `json:"unknownKeyMessage"`
+}
+
 // Both runtimes reject an object-selector key they do not know, so the two key
 // lists have to be one list. Were they to drift, a spec would be accepted by
 // the runtime that lists the key and fail the run on the one that does not, and
 // the difference would only show on the platform nobody ran first.
 // pkg/spec/test/selector-keys.test.ts asserts the SAME file from the web side.
 func TestSelectorKeysMatchTheCrossRuntimeList(t *testing.T) {
-	path, err := filepath.Abs("../../pkg/spec/test/fixtures/selector-keys.json")
-	if err != nil {
-		t.Fatal(err)
+	golden := loadSelectorKeysGolden(t)
+	if got := SelectorKeys(); !slices.Equal(got, golden.Keys) {
+		t.Errorf("native key list\n got=%v\nwant=%v", got, golden.Keys)
 	}
-	body, err := os.ReadFile(path)
-	if err != nil {
-		t.Fatalf("read selector keys: %v", err)
-	}
-	var want []string
-	if err := json.Unmarshal(body, &want); err != nil {
-		t.Fatalf("decode selector keys: %v", err)
-	}
-	if got := SelectorKeys(); !slices.Equal(got, want) {
-		t.Errorf("native key list\n got=%v\nwant=%v", got, want)
+}
+
+// An author who hits this on Android and again on web must read one sentence,
+// not two dialects of it.
+func TestUnknownSelectorKeyMessageMatchesTheCrossRuntimeText(t *testing.T) {
+	golden := loadSelectorKeysGolden(t)
+	if got := UnknownSelectorKeyMessage(golden.UnknownKeyExample); got != golden.UnknownKeyMessage {
+		t.Errorf("native message\n got=%q\nwant=%q", got, golden.UnknownKeyMessage)
 	}
 }
 
@@ -37,3 +44,20 @@ func TestSelectorKeysAreSorted(t *testing.T) {
 		t.Errorf("keys must stay sorted so the two lists compare readably: %v", keys)
 	}
 }
+
+func loadSelectorKeysGolden(t *testing.T) selectorKeysGolden {
+	t.Helper()
+	path, err := filepath.Abs("../../pkg/spec/test/fixtures/selector-keys.json")
+	if err != nil {
+		t.Fatal(err)
+	}
+	body, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatalf("read selector keys: %v", err)
+	}
+	var golden selectorKeysGolden
+	if err := json.Unmarshal(body, &golden); err != nil {
+		t.Fatalf("decode selector keys: %v", err)
+	}
+	return golden
+}