test: implement tests using vitest framework

test/varint.test.js

@@ -0,0 +1,76 @@
+import { describe, it, expect } from "vitest";
+import varint from "../lib/varint.js";
+
+describe("varint.js", () => {
+	it("should encode and decode integers symmetrically (round-trip)", () => {
+		const testValues = [
+			0,
+			1,
+			127, // Max 1-byte
+			128, // Min 2-byte
+			255,
+			16383, // Max 2-byte
+			16384, // Min 3-byte
+			2147483647, // Max signed 32-bit int
+			-1, // Critical edge case (encodes as max unsigned int)
+		];
+
+		testValues.forEach((value) => {
+			const encoded = varint.encodeInt(value);
+			const decoded = varint.decodeInt(encoded, 0);
+			expect(decoded, `Value ${value} failed round-trip`).toBe(value);
+		});
+	});
+
+	it("should decode an integer from a non-zero offset", () => {
+		// [255 (invalid varint), 128 (valid varint), 127 (valid varint)]
+		const buffer = Buffer.from([0xff, 0x80, 0x01, 0x7f]);
+		expect(varint.decodeInt(buffer, 1)).toBe(128);
+	});
+
+	it("should throw an error for a malformed varint that is too long", () => {
+		const invalidBuffer = Buffer.from([0x80, 0x80, 0x80, 0x80, 0x80, 0x80]);
+		expect(() => varint.decodeInt(invalidBuffer, 0)).toThrow(
+			"VarInt is too big"
+		);
+	});
+
+	it("should correctly predict the encoded length of a varint", () => {
+		const boundaries = [0, 127, 128, 16383, 16384, 2097151, 2097152];
+		boundaries.forEach((value) => {
+			const predictedLength = varint.decodeLength(value);
+			const actualLength = varint.encodeInt(value).length;
+			expect(predictedLength).toBe(actualLength);
+		});
+	});
+
+	it("should encode 16-bit unsigned shorts in big-endian format", () => {
+		expect(varint.encodeUShort(0)).toEqual(Buffer.from([0x00, 0x00]));
+		expect(varint.encodeUShort(256)).toEqual(Buffer.from([0x01, 0x00]));
+		expect(varint.encodeUShort(65535)).toEqual(Buffer.from([0xff, 0xff]));
+	});
+
+	it("should correctly assemble and parse a Minecraft handshake packet", () => {
+		const protocolVersion = -1;
+		const virtualHost = "mc.example.com";
+		const port = 25565;
+
+		const payload = Buffer.concat([
+			varint.encodeInt(0),
+			varint.encodeInt(protocolVersion),
+			varint.encodeInt(virtualHost.length),
+			varint.encodeString(virtualHost),
+			varint.encodeUShort(port),
+			varint.encodeInt(1),
+		]);
+
+		const finalPacket = varint.concat([payload]);
+
+		const decodedPacketLength = varint.decodeInt(finalPacket, 0);
+		expect(decodedPacketLength).toBe(payload.length);
+
+		const lengthOfPacketLength = varint.decodeLength(decodedPacketLength);
+		const decodedPayload = finalPacket.subarray(lengthOfPacketLength);
+		expect(decodedPayload).toEqual(payload);
+	});
+});