You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: unparser_test.go
    path of file: ./repos/cel-go/parser
    
    the code of the file until where you have to start completion: // Copyright 2019 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package parser

import (
	"errors"
	"strings"
	"testing"

	"github.com/google/cel-go/common"
	"github.com/google/cel-go/common/ast"
	"github.com/google/cel-go/common/operators"

	"google.golang.org/protobuf/proto"

	exprpb "google.golang.org/genproto/googleapis/api/expr/v1alpha1"
)

func TestUnparse(t *testing.T) {
	tests := []struct {
		name               string
		in                 string
		out                interface{}
		requiresMacroCalls bool
		unparserOptions    []UnparserOption
	}{
		{name: "call_add", in: `a + b - c`},
		{name: "call_and", in: `a && b && c && d && e`},
		{name: "call_and_or", in: `a || b && (c || d) && e`},
		{name: "call_cond", in: `a ? b : c`},
		{name: "call_cond_nested_inner", in: `a ? (c ? d : e) : b`},
		{name: "call_cond_nested_outer", in: `a ? b : c ? d : e`, out: `a ? b : (c ? d : e)`},
		{name: "call_index", in: `a[1]["b"]`},
		{name: "call_index_eq", in: `x["a"].single_int32 == 23`},
		{name: "call_
    
func TestUnparseErrors(t *testing.T) {
	validConstantExpression := &exprpb.Expr{
		ExprKind: &exprpb.Expr_ConstExpr{
			ConstExpr: &exprpb.Constant{
				ConstantKind: &exprpb.Constant_NullValue{},
			},
		},
	}
	tests := []struct {
		name            string
		in              *exprpb.Expr
		err             error
		unparserOptions []UnparserOption
	}{
		{name: "empty_expr", in: &exprpb.Expr{}, err: errors.New("unsupported expression")},
		{
			name: "bad_args",
			in: &exprpb.Expr{
				ExprKind: &exprpb.Expr_CallExpr{
					CallExpr: &exprpb.Expr_Call{
						Function: "_&&_",
						Args:     []*exprpb.Expr{{}, {}},
					},
				},
			},
			err: errors.New("unsupported expression"),
		},
		{
			name: "bad_struct",
			in: &exprpb.Expr{
				ExprKind: &exprpb.Expr_StructExpr{
					StructExpr: &exprpb.Expr_CreateStruct{
						MessageName: "Msg",
						Entries: []*exprpb.Expr_CreateStruct_Entry{
							{KeyKind: &exprpb.Expr_CreateStruct_Entry_FieldKey{FieldKey: "field"}},
						},
					},
				},
			},
			err: errors.New("unsupported expression"),
		},
		{
			name: "bad_map",
			in: &exprpb.Expr{
				ExprKind: &exprpb.Expr_StructExpr{
					StructExpr: &exprpb.Expr_CreateStruct{
						Entries: []*exprpb.Expr_CreateStruct_Entry{
							{KeyKind: &exprpb.Expr_CreateStruct_Entry_FieldKey{FieldKey: "field"}},
						},
					},
				},
			},
			err: errors.New("unsupported expression"),
		},
		{
			name: "bad_index",
			in: &exprpb.Expr{
				ExprKind: &exprpb.Expr_CallExpr{
					CallExpr: &exprpb.Expr_Call{
						Function: "_[_]",
						Args:     []*exprpb.Expr{{}, {}},
					},
				},
			},
			err: errors.New("unsupported expression"),
		},
		{
			name: "bad_unparser_option_wrap_column_zero",
			in:   validConstantExpression,
			err:  errors.New("Invalid unparser option. Wrap column value must be greater than or equal to 1. Got 0 instead"),
			unparserOptions: []UnparserOption{
				WrapOnColumn(0),
			},
		},
		{
			name: "bad_unparser_option_wrap_column_negative",
			in:   validConstantExpression,
			err:  errors.New("Invalid unparser option. Wrap column value must be greater than or equal to 1. Got -1 instead"),
			unparserOptions: []UnparserOption{
				WrapOnColumn(-1),
			},
		},
		{
			name: "bad_unparser_option_unsupported_operator",
			in:   validConstantExpression,
			err:  errors.New("Invalid unparser option. Unsupported operator: bogus"),
			unparserOptions: []UnparserOption{
				WrapOnOperators("bogus"),
			},
		},
		{
			name: "bad_unparser_option_unary_operator",
			in:   validConstantExpression,
			err:  errors.New("Invalid unparser option. Unary operators are unsupported: " + operators.Negate),
			unparserOptions: []UnparserOption{
				WrapOnOperators(operators.Negate),
			},
		},
	}

	for _, tst := range tests {
		tc := tst
		t.Run(tc.name, func(t *testing.T) {
			info := ast.NewSourceInfo(nil)
			e, err := ast.ProtoToExpr(tc.in)
			if err != nil {
				t.Fatalf("ast.ProtoToExpr(%v) failed: %v", tc.in, err)
			}
			out, err := Unparse(e, info, tc.unparserOptions...)
			if err == nil {
				t.Fatalf("Unparse(%v) got %v, wanted error %v", tc.in, out, tc.err)
			}
			if !strings.Contains(err.Error(), tc.err.Error()) {
				t.Errorf("Unparse(%v) got unexpected error: %v, wanted %v", tc.in, err, tc.err)
			}
		})
	}
}