feat: complete remaining Go backend modules

backend/internal/billing/settlement_test.go

@@ -0,0 +1,50 @@
+package billing
+
+import (
+	"context"
+	"testing"
+	"time"
+)
+
+func TestSeedanceActualAmountUsesFrozenTokenPricingAndRoundsUp(t *testing.T) {
+	tests := []struct {
+		resolution string
+		inputVideo bool
+		wantPrice  int64
+		wantAmount int64
+	}{
+		{resolution: "720P", wantPrice: 4600, wantAmount: 6},
+		{resolution: "1080p", inputVideo: true, wantPrice: 3100, wantAmount: 4},
+		{resolution: "4K", wantPrice: 2600, wantAmount: 4},
+	}
+	for _, test := range tests {
+		if got := SeedanceTokenPriceFenPerMillion(test.resolution, test.inputVideo); got != test.wantPrice {
+			t.Fatalf("price(%q, %v) = %d, want %d", test.resolution, test.inputVideo, got, test.wantPrice)
+		}
+		got, err := CalculateSeedanceActualAmountFen(SeedanceActualAmountInput{Resolution: test.resolution, InputVideo: test.inputVideo, CompletionTokens: 1001, MarkupMultiplier: 1.2})
+		if err != nil || got != test.wantAmount {
+			t.Fatalf("amount(%q, %v) = %d, %v; want %d", test.resolution, test.inputVideo, got, err, test.wantAmount)
+		}
+	}
+}
+
+func TestLedgerSettlesSeedanceDeltaWithOneFrozenIdempotencyKey(t *testing.T) {
+	poster := &recordingPoster{result: WalletPosting{LedgerID: "settlement-ledger", CreatedAt: time.Unix(7, 0)}}
+	ledger := Ledger{Poster: poster, NewID: func() string { return "new-ledger" }}
+
+	posting, err := ledger.Settle(context.Background(), SettlementRequest{
+		OrganizationID: "org-1", AccountID: "account-1", JobID: "job-1",
+		DeltaFen: 25, Description: "actual usage charge", Metadata: map[string]any{"operation": "seedance_actual_settlement"},
+	})
+	if err != nil || posting.LedgerID != "settlement-ledger" {
+		t.Fatalf("posting = %#v, err = %v", posting, err)
+	}
+	if poster.params.Kind != "charge" || poster.params.DeltaFen != -25 || poster.params.IdempotencyKey != "job-settlement:job-1" {
+		t.Fatalf("charge params = %#v", poster.params)
+	}
+
+	_, err = ledger.Settle(context.Background(), SettlementRequest{OrganizationID: "org-1", JobID: "job-2", DeltaFen: -9})
+	if err != nil || poster.params.Kind != "refund" || poster.params.DeltaFen != 9 || poster.params.IdempotencyKey != "job-settlement:job-2" {
+		t.Fatalf("refund params = %#v, err = %v", poster.params, err)
+	}
+}