Add xfail tests documenting non-unique generated RSF labels

tests/test_games/label-collision.efg

@@ -0,0 +1,37 @@
+EFG 2 R "label collision counterexample" { "Player 1" }
+"Two 11-action information sets for one player: reduced strategies (1,11) and (11,1) both render label 111"
+
+p "" 1 1 "" { "1" "2" "3" "4" "5" "6" "7" "8" "9" "10" "11" } 0
+p "" 1 2 "" { "1" "2" "3" "4" "5" "6" "7" "8" "9" "10" "11" } 0
+t "" 1 "" { 1 }
+t "" 2 "" { 2 }
+t "" 3 "" { 3 }
+t "" 4 "" { 4 }
+t "" 5 "" { 5 }
+t "" 6 "" { 6 }
+t "" 7 "" { 7 }
+t "" 8 "" { 8 }
+t "" 9 "" { 9 }
+t "" 10 "" { 10 }
+t "" 11 "" { 11 }
+t "" 12 "" { 12 }
+t "" 13 "" { 13 }
+t "" 14 "" { 14 }
+t "" 15 "" { 15 }
+t "" 16 "" { 16 }
+t "" 17 "" { 17 }
+t "" 18 "" { 18 }
+t "" 19 "" { 19 }
+t "" 20 "" { 20 }
+p "" 1 2 "" { "1" "2" "3" "4" "5" "6" "7" "8" "9" "10" "11" } 0
+t "" 21 "" { 21 }
+t "" 22 "" { 22 }
+t "" 23 "" { 23 }
+t "" 24 "" { 24 }
+t "" 25 "" { 25 }
+t "" 26 "" { 26 }
+t "" 27 "" { 27 }
+t "" 28 "" { 28 }
+t "" 29 "" { 29 }
+t "" 30 "" { 30 }
+t "" 31 "" { 31 }

tests/test_strategic.py

@@ -1,3 +1,5 @@
+import io
+
 import pytest
 
 import pygambit as gbt
@@ -73,3 +75,33 @@ def test_game_get_min_payoff():
 def test_game_get_max_payoff():
     game = games.read_from_file("mixed_strategy.nfg")
     assert game.max_payoff == 3
+
+
+@pytest.mark.xfail(
+    reason="Generated reduced-strategy labels are not injective",
+    raises=AssertionError, strict=True,
+)
+def test_generated_strategy_labels_are_unique():
+    """#981 established that a strategy label must be nonempty, valid, and
+    unique among a player's strategies.  Labels generated for reduced
+    strategies bypass the check: two 11-action information sets yield
+    strategies (1, 11) and (11, 1), both rendering as "111"."""
+    g = games.read_from_file("label-collision.efg")
+    labels = [s.label for s in g.players["Player 1"].strategies]
+    dups = sorted({lab for lab in labels if labels.count(lab) > 1})
+    assert len(set(labels)) == len(labels), f"duplicate generated labels: {dups}"
+
+
+@pytest.mark.xfail(
+    reason="Generated reduced-strategy labels are not injective; "
+           "duplicate labels break NFG re-read",
+    raises=ValueError, strict=True,
+)
+def test_game_with_duplicate_generated_labels_roundtrips_through_nfg():
+    """WriteNfgFile serialises the duplicate generated labels;
+    ReadNfgFile then rejects its own output.  FAILS on 16.7.0.
+
+    The game has two 11-action information sets for one player (imperfect
+    recall); reduced strategies (1, 11) and (11, 1) both render as "111"."""
+    g = games.read_from_file("label-collision.efg")
+    gbt.read_nfg(io.StringIO(g.to_nfg()))