diff --git a/tests/test_leftover_axis_tick_share_contract.py b/tests/test_leftover_axis_tick_share_contract.py
new file mode 100644
index 000000000..e2e27f2d4
--- /dev/null
+++ b/tests/test_leftover_axis_tick_share_contract.py
@@ -0,0 +1,29 @@
+"""Executable contract for report leftover-axis tick share captions."""
+
+from pathlib import Path
+
+
+ROOT = Path(__file__).resolve().parents[1]
+BADGE_SOURCE = ROOT / "frontend" / "src" / "leftoverMapAxisBadge.ts"
+
+
+def test_report_axis_tick_keeps_axis_share_independent_of_singular() -> None:
+    """A report leftover-axis tick may name persisted share when singular evidence is absent."""
+    assert BADGE_SOURCE.exists(), "report-axis badge helper is missing"
+    source = BADGE_SOURCE.read_text(encoding="utf-8")
+
+    assert "leftoverMapAxisTickBadge" in source
+    assert "leftover axis {axis} tick {value} {share}%" in source
+    assert "leftover axis {axis} tick {value} σ {singular} {share}%" in source
+
+
+def test_report_axis_tick_never_infers_share_from_singular() -> None:
+    """Share-only, singular-only, combined, and empty states remain persisted-data decisions."""
+    assert BADGE_SOURCE.exists(), "report-axis badge helper is missing"
+    source = BADGE_SOURCE.read_text(encoding="utf-8")
+
+    assert "Number.isFinite" in source
+    assert "leftover_share" in source
+    assert "formatLeftoverMapPlotAxisSingular" in source
+    assert "Math.sqrt" not in source
+    assert "Math.max" not in source