Add test coverage for parent(0) and parent(-3) edge cases

Co-authored-by: mikefarah <[email protected]>

Author: Copilot

pkg/yqlib/operator_parent_test.go

@@ -65,6 +65,15 @@ var parentOperatorScenarios = []expressionScenario{
 			"D0, P[a], (!!map)::b:\n    c: cat\n",
 		},
 	},
+	{
+		description: "boundary negative",
+		skipDoc:     true,
+		document:    "a:\n  b:\n    c: cat\n",
+		expression:  `.a.b.c | parent(-3)`,
+		expected: []string{
+			"D0, P[a b], (!!map)::c: cat\n",
+		},
+	},
 	{
 		description: "large negative",
 		skipDoc:     true,
@@ -74,6 +83,15 @@ var parentOperatorScenarios = []expressionScenario{
 			"D0, P[a b c], (!!str)::cat\n",
 		},
 	},
+	{
+		description: "parent zero",
+		skipDoc:     true,
+		document:    "a:\n  b:\n    c: cat\n",
+		expression:  `.a.b.c | parent(0)`,
+		expected: []string{
+			"D0, P[a b c], (!!str)::cat\n",
+		},
+	},
 	{
 		description: "large positive",
 		skipDoc:     true,