mobile: strengthen the PartLabels fallback test and count bounds

2 files changed, 20 insertions, 4 deletions

diff --git a/mobile/mobile.go b/mobile/mobile.go
index d863463..d91831c 100644
--- a/mobile/mobile.go
+++ b/mobile/mobile.go
@@ -8,7 +8,9 @@
 // document with the day's identity and rendered Mass readings. All liturgical
 // computation and text resolution happens here, in the exact validated lectio
 // engine — the app does none of it. Keep every exported signature to types
-// gomobile can marshal (string in, string out): that is why the payload is JSON.
+// gomobile can marshal -- strings and ints only -- with JSON as the payload
+// format for everything structured. A Go int parameter (e.g. Days' count)
+// surfaces on the Kotlin side as a long, not an Int.
 package mobile
 
 import (
diff --git a/mobile/mobile_test.go b/mobile/mobile_test.go
index 1a115f3..cf75b7f 100644
--- a/mobile/mobile_test.go
+++ b/mobile/mobile_test.go
@@ -111,6 +111,7 @@ func TestDaysRejectsBadInput(t *testing.T) {
 		count int
 	}{
 		{"not-a-date", 7}, {"2026-08-01", 0}, {"2026-08-01", -1}, {"2026-08-01", 400},
+		{"2026-08-01", 367}, // one past the documented upper bound
 	} {
 		if got := Days(c.start, c.count, "of", "pl"); got != "[]" {
 			t.Errorf("Days(%q, %d) = %s, want []", c.start, c.count, got)
@@ -118,6 +119,16 @@ func TestDaysRejectsBadInput(t *testing.T) {
 	}
 }
 
+// count's documented range is 1..366; 367 (above) is the first invalid value
+// and 366 (here) is the last valid one -- the boundary an off-by-one would
+// actually live on.
+func TestDaysAcceptsUpperBoundCount(t *testing.T) {
+	a := decodeDays(t, Days("2026-01-01", 366, "of", "en"))
+	if len(a) != 366 {
+		t.Errorf("got %d elements, want 366", len(a))
+	}
+}
+
 func BenchmarkDaysWeek(b *testing.B) {
 	for i := 0; i < b.N; i++ {
 		Days("2026-07-27", 7, "of", "pl")
@@ -163,8 +174,11 @@ func TestPartLabelsMatchesWhatTheEngineEmits(t *testing.T) {
 }
 
 func TestPartLabelsUnknownForm(t *testing.T) {
-	// An unknown form is treated as the modern one, matching lectByForm.
-	if got := PartLabels("nonsense", "en"); got == "[]" {
-		t.Error("unknown form should fall back to the modern lectionary, not empty")
+	// An unknown form is treated as the modern one, matching lectByForm: the
+	// fallback must be byte-identical to "of", not merely non-empty.
+	got := PartLabels("nonsense", "en")
+	want := PartLabels("of", "en")
+	if got != want {
+		t.Errorf("PartLabels(\"nonsense\", \"en\") = %s, want %s (same as \"of\")", got, want)
 	}
 }