Add non-proto field test.

checker/cost.go

@@ -340,8 +340,11 @@ func (c *coster) costSelect(e *exprpb.Expr) CostEstimate {
 	sel := e.GetSelectExpr()
 	var sum CostEstimate
 	if sel.GetTestOnly() {
-		sum.Min = 1
-		sum.Max = 1
+		// recurse, but do not add any cost
+		// this is equivalent to how evalTestOnly increments the runtime cost counter
+		// but does not add any additional cost for the qualifier, except here we do
+		// the reverse (ident adds cost)
+		sum = sum.Add(c.cost(sel.GetOperand()))
 		return sum
 	}
 	sum = sum.Add(c.cost(sel.GetOperand()))

interpreter/runtimecost_test.go

@@ -317,6 +317,19 @@ func TestRuntimeCost(t *testing.T) {
 				},
 			},
 		},
+		{
+			name:  "select: non-proto field test",
+			expr:  `has(input.testAttr.nestedAttr)`,
+			decls: []*exprpb.Decl{decls.NewVar("input", nestedMap)},
+			want:  2,
+			in: map[string]any{
+				"input": map[string]any{
+					"testAttr": map[string]any{
+						"nestedAttr": "0",
+					},
+				},
+			},
+		},
 		{
 			name:         "estimated function call",
 			expr:         `input.getFullYear()`,