Add tests for Node.is_subgame_root

This adds better tests for `Node.is_subgame_root`.
In particular, it adds a test for a known case in which the existing implementation fails
(an absent-minded information set that is not at the root of the game tree).

Closes #583

---------

Co-authored-by: Ted Turocy <drarbiter@gmail.com>

Author: d-kad

tests/test_games/AM-driver-subgame.efg

@@ -0,0 +1,10 @@
+EFG 2 R "Untitled Extensive Game" { "Player 1" "Player 2" }
+""
+
+p "" 1 1 "" { "1" "2" } 0
+p "" 1 1 "" { "1" "2" } 0
+t "" 1 "Outcome 1" { 1, -1 }
+p "" 2 1 "" { "1" "2" } 0
+t "" 2 "Outcome 2" { 2, -2 }
+t "" 3 "Outcome 3" { 3, -3 }
+t "" 4 "Outcome 4" { 4, -4 }

tests/test_games/subgames.efg

@@ -0,0 +1,40 @@
+EFG 2 R "Untitled Extensive Game" { "Player 1" "Player 2" }
+""
+
+p "" 2 1 "" { "1" "2" } 0
+p "" 1 1 "" { "1" "2" } 0
+t "" 1 "Outcome 1" { 1, -1 }
+t "" 2 "Outcome 2" { 2, -2 }
+p "" 1 2 "" { "1" "2" } 0
+p "" 2 2 "" { "1" "2" } 0
+t "" 3 "Outcome 3" { 3, -3 }
+p "" 1 3 "" { "1" "2" } 0
+t "" 4 "Outcome 4" { 4, -4 }
+t "" 5 "Outcome 5" { 5, -5 }
+p "" 2 2 "" { "1" "2" } 0
+p "" 2 3 "" { "1" "2" } 0
+p "" 1 4 "" { "1" "2" } 0
+p "" 2 4 "" { "1" "2" } 0
+t "" 6 "Outcome 6" { 6, -6 }
+t "" 7 "Outcome 7" { 7, -7 }
+t "" 8 "Outcome 8" { 8, -8 }
+p "" 1 5 "" { "1" "2" } 0
+p "" 2 6 "" { "1" "2" } 0
+t "" 9 "Outcome 9" { 9, -9 }
+t "" 10 "Outcome 10" { 10, -10 }
+p "" 2 6 "" { "1" "2" } 0
+p "" 1 7 "" { "1" "2" } 0
+p "" 2 5 "" { "1" "2" } 0
+p "" 1 4 "" { "1" "2" } 0
+t "" 11 "Outcome 11" { 11, -11 }
+t "" 12 "Outcome 12" { 12, -12 }
+p "" 1 4 "" { "1" "2" } 0
+t "" 13 "Outcome 13" { 13, -13 }
+t "" 14 "Outcome 14" { 14, -14 }
+t "" 15 "Outcome 15" { 15, -15 }
+p "" 1 7 "" { "1" "2" } 0
+t "" 16 "Outcome 16" { 16, -16 }
+t "" 17 "Outcome 17" { 17, -17 }
+p "" 1 6 "" { "1" "2" } 0
+t "" 18 "Outcome 18" { 18, -18 }
+t "" 19 "Outcome 19" { 19, -19 }

tests/test_node.py

@@ -86,11 +86,30 @@ def test_is_successor_of():
         game.root.is_successor_of(game.players[0])
 
 
-def test_is_subgame_root():
-    """Test whether nodes are correctly labeled as roots of proper subgames."""
-    game = games.read_from_file("basic_extensive_game.efg")
-    assert game.root.is_subgame_root
-    assert not game.root.children[0].is_subgame_root
+@pytest.mark.parametrize("game, expected_result", [
+    # Games without Absent-Mindedness for which the legacy method is known to be correct.
+    (games.read_from_file("wichardt.efg"), {0}),
+    (games.read_from_file("e02.efg"), {0, 2, 4}),
+    (games.read_from_file("subgames.efg"), {0, 1, 4, 7, 11, 13, 34}),
+
+    pytest.param(
+        games.read_from_file("AM-driver-subgame.efg"),
+        {0, 3},  # The correct set of subgame roots
+        marks=pytest.mark.xfail(
+            reason="Current method does not detect roots of proper subgames "
+                   "that are members of AM-infosets."
+        )
+    ),
+])
+def test_legacy_is_subgame_root_set(game: gbt.Game, expected_result: set):
+    """
+    Tests the legacy `node.is_subgame_root` against an expected set of nodes.
+    Includes both passing cases and games with Absent-Mindedness where it is expected to fail.
+    """
+    list_nodes = list(game.nodes)
+    expected_roots = {list_nodes[i] for i in expected_result}
+    legacy_roots = {node for node in game.nodes if node.is_subgame_root}
+    assert legacy_roots == expected_roots
 
 
 def test_append_move_error_player_actions():