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	detect en passant, add some tests for it - chess-puzzles - chess puzzle book ge…
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	---
	commit 64c4e3aaecf348c2cb7c61f5569cae1a820d20db
	parent d69d3ff1075f952ebdd45af40e7580bb3003721f
	Author: Hiltjo Posthuma <[email protected]>
	Date: Wed, 20 Dec 2023 20:35:16 +0100

	detect en passant, add some tests for it

	Diffstat:
	M fen_to_svg.c \| 21 ++++++++++++++++++---
	M tests.sh \| 17 +++++++++++++++--

	2 files changed, 33 insertions(+), 5 deletions(-)
	---
	diff --git a/fen_to_svg.c b/fen_to_svg.c
	@@ -1,4 +1,3 @@
	-/* TODO: write some test-cases for parsing and output FEN */
	/* TODO: option to flip board? */

	#include <ctype.h>
	@@ -120,8 +119,6 @@ showboardfen(void)
	putchar('-');
	}
	printf(" %d %d", halfmove, movenumber);
	-
	- /* ? TODO: detect en passant, invalid castling etc? */
	}

	void
	@@ -592,6 +589,24 @@ main(int argc, char *argv[])
	black_can_castle[0] = 0;
	}

	+ /* the en passant square resets after a move */
	+ enpassantsquare[0] = -1;
	+ enpassantsquare[1] = -1;
	+ /* moved 2 squares and there is an opponent pawn next …
	+ if (piece == 'P' && y == 6 && y2 == 4) {
	+ if (getpiece(x - 1, y2) == 'p' \|\|
	+ getpiece(x + 1, y2) == 'p') {
	+ enpassantsquare[0] = x;
	+ enpassantsquare[1] = 5;
	+ }
	+ } else if (piece == 'p' && y == 1 && y2 == 3) {
	+ if (getpiece(x - 1, y2) == 'P' \|\|
	+ getpiece(x + 1, y2) == 'P') {
	+ enpassantsquare[0] = x;
	+ enpassantsquare[1] = 2;
	+ }
	+ }
	+
	/* possible promotion: queen, knight, bishop */
	if (s == 'q' \|\| s == 'n' \|\| *s == 'b') {
	if (side_to_move == 'w')
	diff --git a/tests.sh b/tests.sh
	@@ -63,5 +63,18 @@ testfen 'r3kbr1/pp2qppp/n1p2n2/3p1B2/3P1B2/4QN1b/PPP2PPP/RN2…
	'r3kbr1/pp2qppp/n1p2n2/3p4/3P1B2/3BQN1b/PPP2PPP/RN2K2R w KQq - 8 12'\
	'd3f5'

	-# TODO: test halfmove
	-# TODO: test enpassant
	+# test en passant: move white pawn g2 to g4, enpassant square becomes g3.
	+testfen 'r4k1r/ppppp1pp/8/8/5pP1/4P3/PPPP1P1P/R3K2R b - g3 0 4'\
	+ 'r4k1r/ppppp1pp/8/8/5p2/4P3/PPPP1PPP/R3K2R w - - 0 4'\
	+ 'g2g4'
	+# moving 2 squares near a pawn, but not en passant.
	+testfen 'r4k1r/ppppp1p1/8/5p2/6P1/4P2p/PPPP1P1P/R3K2R b - - 0 6'\
	+ 'r4k1r/ppppp1p1/8/5p2/8/4P2p/PPPP1PPP/R3K2R w - - 0 6'\
	+ 'g2g4'
	+# test en passant for black.
	+testfen 'r4k1r/ppp1p1p1/8/2Pp1p2/6P1/4P2p/PP1P1P1P/R3K2R w - d6 0 9'\
	+ 'r4k1r/ppppp1p1/8/2P2p2/6P1/4P2p/PP1P1P1P/R3K2R b - - 0 8'\
	+ 'd7d5'
	+testfen 'r4k1r/p1ppp1p1/8/1pP2p2/6P1/4P2p/PP1P1P1P/R3K2R w - b6 0 9'\
	+ 'r4k1r/ppppp1p1/8/2P2p2/6P1/4P2p/PP1P1P1P/R3K2R b - - 0 8'\
	+ 'b7b5'