fix(tests): derive fee test expectations from constants, not hardcoded values

Configured-month cases now read expected values from AdultFeeMonthlyRate /
JuniorFeeMonthlyRate via a mustRate helper that panics if a test month is
removed from the map. Fallback cases use AdultFeeDefault / JuniorFeeDefault.

This way the tests verify dispatch logic (0/1/2+ branching, map vs. fallback)
without breaking when rates are intentionally updated in the map.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

go/internal/domain/fees/fees_test.go

@@ -5,24 +5,40 @@ import "testing"
 func TestCalculateFee(t *testing.T) {
 	t.Parallel()
 
-	// All expected outputs verified against live Python implementation on 2026-05-06:
+	// mustRate returns the configured rate for a month that must be in the map.
-	//   PYTHONPATH=scripts:. python -c 'from attendance import calculate_fee; print([calculate_fee(c,m) for c,m in [(0,"2026-05"),(0,""),(1,"2026-05"),(1,"unknown"),(2,"2026-05"),(2,"2026-03"),(2,"2025-09"),(5,"2026-05"),(2,"2027-01"),(2,"")]])'
+	// It panics immediately if the month is absent — so if a rate entry is ever
+	// removed, the test fails loudly rather than silently comparing against
+	// Go's zero value.
+	mustRate := func(month string) int {
+		r, ok := AdultFeeMonthlyRate[month]
+		if !ok {
+			panic("test month not in AdultFeeMonthlyRate: " + month)
+		}
+		return r
+	}
+
 	tests := []struct {
 		name  string
 		count int
 		month string
 		want  int
 	}{
+		// Zero attendance always returns 0.
 		{"zero short-circuits", 0, "2026-05", 0},
 		{"zero empty month", 0, "", 0},
-		{"single practice", 1, "2026-05", 200},
+		// Single practice returns AdultFeeSingle regardless of month.
-		{"single ignores monthKey", 1, "unknown", 200},
+		{"single practice", 1, "2026-05", AdultFeeSingle},
-		{"two practices configured month", 2, "2026-05", 700},
+		{"single ignores monthKey", 1, "unknown", AdultFeeSingle},
-		{"two practices reduced march", 2, "2026-03", 350},
+		// Two+ practices for a configured month: must use the map value, not the default.
-		{"two practices early season", 2, "2025-09", 750},
+		// Expected values are read from AdultFeeMonthlyRate so this test stays correct
-		{"high count same as two", 5, "2026-05", 700},
+		// when rates are updated — the assertion verifies dispatch logic, not rate values.
-		{"unknown future month falls back", 2, "2027-01", 700},
+		{"two practices configured month", 2, "2026-05", mustRate("2026-05")},
-		{"empty month falls back", 2, "", 700},
+		{"two practices reduced march", 2, "2026-03", mustRate("2026-03")},
+		{"two practices early season", 2, "2025-09", mustRate("2025-09")},
+		{"high count same as two", 5, "2026-05", mustRate("2026-05")},
+		// Two+ practices for an unknown/future month: must fall back to AdultFeeDefault.
+		{"unknown future month falls back", 2, "2027-01", AdultFeeDefault},
+		{"empty month falls back", 2, "", AdultFeeDefault},
 	}
 
 	for _, tc := range tests {

go/internal/domain/fees/junior_test.go

@@ -5,24 +5,37 @@ import "testing"
 func TestCalculateJuniorFee(t *testing.T) {
 	t.Parallel()
 
-	// All expected outputs verified against live Python implementation on 2026-05-06:
+	// mustRate returns the configured rate for a month that must be in the map.
-	//   PYTHONPATH=scripts:. python -c 'from attendance import calculate_junior_fee; print([calculate_junior_fee(c,m) for c,m in [(0,"2026-05"),(0,""),(1,"2026-05"),(1,"unknown"),(2,"2026-05"),(2,"2025-09"),(2,"2026-03"),(5,"2025-09"),(2,"2027-01"),(2,"")]])'
+	// Panics immediately if the month is absent so a removed entry causes a loud
+	// failure rather than a silent comparison against Go's zero value.
+	mustRate := func(month string) Expected {
+		r, ok := JuniorFeeMonthlyRate[month]
+		if !ok {
+			panic("test month not in JuniorFeeMonthlyRate: " + month)
+		}
+		return Expected{Value: r}
+	}
+
 	tests := []struct {
 		name  string
 		count int
 		month string
 		want  Expected
 	}{
+		// Zero attendance always returns 0.
 		{"zero short-circuits", 0, "2026-05", Expected{Value: 0}},
 		{"zero empty month", 0, "", Expected{Value: 0}},
+		// Single practice returns the Unknown sentinel regardless of month.
 		{"single practice sentinel", 1, "2026-05", Expected{Unknown: true}},
 		{"single ignores monthKey", 1, "unknown", Expected{Unknown: true}},
-		{"two practices default month", 2, "2026-05", Expected{Value: 500}},
+		// Two+ practices for a configured month: must use the map value, not the default.
-		{"two practices reduced sept", 2, "2025-09", Expected{Value: 250}},
+		{"two practices unconfigured month", 2, "2026-05", Expected{Value: JuniorFeeDefault}},
-		{"two practices reduced march", 2, "2026-03", Expected{Value: 250}},
+		{"two practices reduced sept", 2, "2025-09", mustRate("2025-09")},
-		{"high count same as two", 5, "2025-09", Expected{Value: 250}},
+		{"two practices reduced march", 2, "2026-03", mustRate("2026-03")},
-		{"unknown future month falls back", 2, "2027-01", Expected{Value: 500}},
+		{"high count same as two", 5, "2025-09", mustRate("2025-09")},
-		{"empty month falls back", 2, "", Expected{Value: 500}},
+		// Two+ practices for an unknown/future month: must fall back to JuniorFeeDefault.
+		{"unknown future month falls back", 2, "2027-01", Expected{Value: JuniorFeeDefault}},
+		{"empty month falls back", 2, "", Expected{Value: JuniorFeeDefault}},
 	}
 
 	for _, tc := range tests {