feat(shared): add signed percent and percentage-point formatters (WealthLedger/main#54)

src/shared/lib/display.test.ts

@@ -3,12 +3,22 @@ import { describe, expect, it } from "vitest";
 import {
 	formatDate,
 	formatMoney,
+	formatPercentagePoints,
+	formatSignedPercent,
 	formatSnapshotDay,
 	formatSnapshotTime,
 	instrumentLogoUrl,
 } from "./display";
 
 describe("shared display helpers", () => {
+	it("formats signed rates as percentages and percentage points without negative zero", () => {
+		expect(formatSignedPercent("0.151")).toBe("+15,1 %");
+		expect(formatSignedPercent("-0.15149")).toBe("−15,1 %");
+		expect(formatSignedPercent("0")).toBe("0,0 %");
+		expect(formatSignedPercent("-0.00049")).toBe("0,0 %");
+		expect(formatPercentagePoints("0.043")).toBe("+4,3 п.п.");
+		expect(formatPercentagePoints("-0.0435")).toBe("−4,4 п.п.");
+	});
 	it("uses padded Russian dates and preserves the UTC date of timestamps", () => {
 		expect(formatDate("2027-09-10")).toBe("10.09.2027");
 		expect(formatDate("2024-02-29")).toBe("29.02.2024");