En passant target squares not properly generated in FEN EPD

[B1tWhys]

Hello,

Thanks for writing this library, it's extremely useful! The only thing I'm having trouble with is that it doesn't seem like en passant target squares are correctly handled by the FEN generation code. Here's an example:

import {Chess} from "chessops/chess";
import {makeFen} from "chessops/fen";
import {parseSan} from "chessops/san";

describe("When generating FEN", () => {
    test("en passant target square is in EPD", () => {
        const chess = Chess.default();
        chess.play(parseSan(chess, "a4"));
        expect(makeFen(chess.toSetup())).toBe("rnbqkbnr/pppppppp/8/8/P7/8/1PPPPPPP/RNBQKBNR b KQkq a3 0 1");
    });
}

which fails with:

Error: expect(received).toBe(expected) // Object.is equality

Expected: "rnbqkbnr/pppppppp/8/8/P7/8/1PPPPPPP/RNBQKBNR b KQkq a3 0 1"
Received: "rnbqkbnr/pppppppp/8/8/P7/8/1PPPPPPP/RNBQKBNR b KQkq - 0 1"

[niklasf]

Hi, like on Lichess and similar to X-FEN, the en passant square is only included if there is actually a legal en passant move. If you really need it, you can force it as follows:

const setup = chess.toSetup();
setup.epSquare = chess.epSquare;
makeFen(chess.toSetup())

[B1tWhys]

Oh, that makes sense & is completely fine for my needs; I just need to adjust some of my my test cases a little. Thanks for the very fast response (and wonderful library)!