chore: add tests

src/utils/decodeBase64ToUTF8.spec.ts

@@ -0,0 +1,25 @@
+import { describe, expect, it } from "vitest"
+
+import { decodeBase64ToUTF8, encodeUTF8ToBase64 } from "./decodeBase64ToUTF8"
+
+describe("base64 ↔ UTF-8 round-trip", () => {
+  it.each([
+    ["ASCII", "Hello, world!"],
+    ["multi-byte UTF-8", "Café résumé naïve"],
+    ["CJK characters", "こんにちは世界"],
+    ["emoji", "👋 🌍 🎉"],
+    ["empty string", ""],
+    ["newlines and whitespace", "line1\nline2\tend"],
+    ["markdown content", "# Title\n\n- [[link]]\n- **bold**"]
+  ])("round-trips %s", (_label, input) => {
+    expect(decodeBase64ToUTF8(encodeUTF8ToBase64(input))).toBe(input)
+  })
+
+  it("encodes ASCII to standard base64", () => {
+    expect(encodeUTF8ToBase64("hi")).toBe("aGk=")
+  })
+
+  it("decodes standard base64 to ASCII", () => {
+    expect(decodeBase64ToUTF8("aGk=")).toBe("hi")
+  })
+})