Add v3 protocol test suite

[sleeyax]

Closes socketio/socket.io-protocol#30.

TODO (help welcome):

• Add test for a payload with binary data (not base64 encoded)

Let me know if something else is missing or should be updated.

[darrachequesne]

Awesome, thanks! Merged as 723c7ba.

I have added a test with binary:

engine.io-protocol/test-suite/test-suite.js

Lines 244 to 280 in 723c7ba

	it("sends and receives a payload containing plain text and binary packets (binary)", async () => {
	const sid = await initLongPollingSession(true);
	const pushResponse = await fetch(
	`${URL}/engine.io/?EIO=3&transport=polling&sid=${sid}`,
	{
	method: "post",
	body: "6:4hello10:b4AQIDBA==",
	}
	);
	expect(pushResponse.status).to.eql(200);
	const postContent = await pushResponse.text();
	expect(postContent).to.eql("ok");
	const pollResponse = await fetch(
	`${URL}/engine.io/?EIO=3&transport=polling&sid=${sid}`
	);
	expect(pollResponse.status).to.eql(200);
	const buffer = await pollResponse.arrayBuffer();
	// 0 => string
	// 6 => byte length
	// 255 => delimiter
	// 52 => 4 (MESSAGE packet type)
	// 104 101 108 108 111 => "hello"
	// 1 => binary
	// 5 => byte length
	// 255 => delimiter
	// 4 => 4 (MESSAGE packet type)
	// 1 2 3 4 => binary message
	expect(buffer).to.eql(Uint8Array.from([0, 6, 255, 52, 104, 101, 108, 108, 111, 1, 5, 255, 4, 1, 2, 3, 4]).buffer);
	});