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: vec_test.go
    path of file: ./repos/cockroach/pkg/col/coldata
    
    the code of the file until where you have to start completion: // Copyright 2019 The Cockroach Authors.
//
// Use of this software is governed by the Business Source License
// included in the file licenses/BSL.txt.
//
// As of the Change Date specified in that file, in accordance with
// the Business Source License, use of this software will be governed
// by the Apache License, Version 2.0, included in the file
// licenses/APL.txt.

package coldata_test

import (
	"fmt"
	"testing"

	"github.com/cockroachdb/cockroach/pkg/col/coldata"
	"github.com/cockroachdb/cockroach/pkg/col/coldatatestutils"
	"github.com/cockroachdb/cockroach/pkg/sql/types"
	"github.com/cockroachdb/cockroach/pkg/util/leaktest"
	"github.com/cockroachdb/cockroach/pkg/util/randutil"
	"github.com/stretchr/testify/require"
)

func TestMemColumnWindow(t *testing.T) {
	defer leaktest.AfterTest(t)()

	rng, _ := 
    
func TestCopy(t *testing.T) {
	// TODO(asubiotto): Test nulls.
	var typ = types.Int

	src := coldata.NewMemColumn(typ, coldata.BatchSize(), coldata.StandardColumnFactory)
	srcInts := src.Int64()
	for i := range srcInts {
		srcInts[i] = int64(i + 1)
	}
	sel := make([]int, len(src.Int64()))
	for i := range sel {
		sel[i] = i
	}

	sum := func(ints []int64) int {
		s := 0
		for _, i := range ints {
			s += int(i)
		}
		return s
	}

	testCases := []struct {
		name        string
		args        coldata.SliceArgs
		expectedSum int
	}{
		{
			name:        "CopyNothing",
			args:        coldata.SliceArgs{},
			expectedSum: 0,
		},
		{
			name: "CopyBatchSizeMinus1WithOffset1",
			args: coldata.SliceArgs{
				// Use DestIdx 1 to make sure that it is respected.
				DestIdx:   1,
				SrcEndIdx: coldata.BatchSize() - 1,
			},
			// expectedSum uses sum of positive integers formula.
			expectedSum: (coldata.BatchSize() - 1) * coldata.BatchSize() / 2,
		},
		{
			name: "CopyWithSel",
			args: coldata.SliceArgs{
				Sel:         sel[1:],
				DestIdx:     25,
				SrcStartIdx: 1,
				SrcEndIdx:   2,
			},
			// We'll have just the third element in the resulting slice.
			expectedSum: 3,
		},
	}

	for _, tc := range testCases {
		if tc.args.DestIdx+(tc.args.SrcEndIdx-tc.args.SrcStartIdx) > coldata.BatchSize() {
			continue
		}
		tc.args.Src = src
		t.Run(tc.name, func(t *testing.T) {
			dest := coldata.NewMemColumn(typ, coldata.BatchSize(), coldata.StandardColumnFactory)
			dest.Copy(tc.args)
			destInts := dest.Int64()
			firstNonZero := 0
			for i := range destInts {
				if destInts[i] != 0 {
					firstNonZero = i
					break
				}
			}
			// Verify that Copy started copying where we expected it to.
			require.Equal(t, tc.args.DestIdx, firstNonZero)
			require.Equal(t, tc.expectedSum, sum(destInts))
		})
	}
}