1 files changed, 46 insertions, 0 deletions
diff --git a/internal/calendar/temporal_ef_test.go b/internal/calendar/temporal_ef_test.go
index d930cc7..c1571b0 100644
--- a/internal/calendar/temporal_ef_test.go
+++ b/internal/calendar/temporal_ef_test.go
@@ -360,3 +360,49 @@ func TestTemporalEFPassiontideWeeks(t *testing.T) {
 		}
 	}
 }
+
+// TestTemporalEFHolyName pins RG 17(a): "festum Ss.mi Nominis Iesu,
+// celebrandum dominica quae occurrit a die 2 ad 5 ianuarii, secus die 2
+// ianuarii" -- the Most Holy Name of Jesus is kept on the Sunday falling 2-5
+// January, and when no Sunday falls in that window, on 2 January instead.
+//
+// The FALLBACK is the half worth testing hardest. The window is four days
+// wide, so in about three years in seven no Sunday lands in it; without the
+// fallback there is simply no Holy Name office in those years, which is a
+// missing II-class feast rather than a misnamed one.
+func TestTemporalEFHolyName(t *testing.T) {
+	// Years where a Sunday does fall in the window, at each end of it.
+	for _, c := range []struct{ date, slug string }{
+		{"2026-01-04", "ef-holy-name-sunday"}, // Sunday the 4th
+		{"2027-01-03", "ef-holy-name-sunday"}, // Sunday the 3rd
+		{"2028-01-02", "ef-holy-name-sunday"}, // Sunday the 2nd -- the window's first day
+	} {
+		if got := temporalEF(d(c.date)).Cel.Slug; got != c.slug {
+			t.Errorf("%s: slug = %q, want %q", c.date, got, c.slug)
+		}
+	}
+	// 2029: no Sunday falls 2-5 January, so 2 January carries the feast.
+	if got := temporalEF(d("2029-01-02")).Cel.Slug; got != "ef-holy-name" {
+		t.Errorf("2029-01-02: slug = %q, want ef-holy-name -- no Sunday falls 2-5 January "+
+			"that year, so RG 17(a)'s \"secus die 2 ianuarii\" applies", got)
+	}
+	// And in a year where a Sunday DOES fall in the window, 2 January must NOT
+	// also carry it -- the fallback is an alternative, not an addition.
+	if got := temporalEF(d("2026-01-02")).Cel.Slug; got == "ef-holy-name" {
+		t.Errorf("2026-01-02: slug = %q, but the Sunday the 4th carries the feast that "+
+			"year -- the fallback must not fire as well", got)
+	}
+	// Sanity on the helper itself, across the whole fixture range: every year
+	// gets the feast exactly once, by one shape or the other.
+	for y := 2005; y <= 2050; y++ {
+		n := 0
+		for day := 2; day <= 5; day++ {
+			if s := temporalEF(time.Date(y, time.January, day, 0, 0, 0, 0, time.UTC)).Cel.Slug; s == "ef-holy-name" || s == "ef-holy-name-sunday" {
+				n++
+			}
+		}
+		if n != 1 {
+			t.Errorf("%d: the Holy Name appears %d times in 2-5 January, want exactly 1", y, n)
+		}
+	}
+}