[perft] A script that checks a list of positions against known node counts

A small Python script that reads a JSON list of positions and their known Perft
node counts to a certain depth, then invokes the Perft program for each position
and validates the output.

Peter Ellis Jones shared such a JSON list on GitHub. Import that file.

perft/scripts/check-positions

@@ -0,0 +1,80 @@
+#!/usr/bin/env python3
+# Eryn Wells <eryn@erynwells.me>
+
+'''
+New script.
+'''
+
+import argparse
+import json
+import subprocess
+
+
+def run_perft(fen, depth, expected_nodes_count):
+    result = subprocess.run(
+        [
+            'cargo',
+            'run',
+            '--',
+            '--fen', fen,
+            str(depth)
+        ],
+        capture_output=True,
+        check=True,
+        text=True
+    )
+
+    nodes_count = 0
+    for line in result.stdout.splitlines():
+        if line.startswith('nodes='):
+            (_, nodes_count) = line.split('=')
+            nodes_count = int(nodes_count)
+
+    return nodes_count
+
+
+def parse_args(argv, *a, **kw):
+    parser = argparse.ArgumentParser(*a, **kw)
+    parser.add_argument('-c', '--continue', dest='should_continue',
+                        action='store_true')
+    parser.add_argument('file')
+    args = parser.parse_args(argv)
+    return args
+
+
+def main(argv):
+    args = parse_args(argv[1:], prog=argv[0])
+
+    items = []
+    with open(args.file, 'r') as f:
+        items = json.load(f)
+
+    should_continue = args.should_continue
+
+    for item in items:
+        fen = item['fen']
+        depth = item['depth']
+        expected_nodes_count = int(item['nodes'])
+
+        print('---')
+        print(f'fen={fen}')
+        print(f'expected-nodes={expected_nodes_count}')
+
+        nodes_count = run_perft(fen, depth, expected_nodes_count)
+        print(f'nodes={nodes_count}')
+
+        did_pass = nodes_count == expected_nodes_count
+        if did_pass:
+            print('result=PASS')
+        else:
+            print('result=FAIL')
+
+        if not did_pass and not should_continue:
+            return -1
+        
+    return 0 
+
+
+if __name__ == '__main__':
+    import sys
+    sys.exit(main(sys.argv))