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: dtrtrs.go
    path of file: ./repos/gonum/lapack/testlapack
    
    the code of the file until where you have to start completion: // Copyright ©2020 The Gonum Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package testlapack

import (
	"fmt"
	"math"
	"testing"

	"golang.org/x/exp/rand"

	"gonum.org/v1/gonum/blas"
	"gonum.org/v1/gonum/blas/blas64"
	"gonum.org/v1/gonum/floats"
	"gonum.org/v1/gonum/lapack"
)

type Dtrtrser interface {
	Dtrtrs(uplo blas.Uplo, trans blas.Transpose, diag blas.Diag, n, nrhs int, a []float64, lda int, b []float64, ldb int) bool
}

func DtrtrsTest(t *testing.T, impl Dtrtrser) {
	rnd := rand.New(rand.NewSource(1))

	for _, trans := range []blas.Transpose{blas.NoTrans, blas.Trans, blas.ConjTrans} {
		name := transToString(trans)
		t.Run(name, func(t *testing.T) {
			for _, uplo := range []blas.Uplo{blas.Upper, blas.Lower} {
				for _, diag := range []blas.Diag{blas.Unit, blas.NonUnit} {
					for _, n := range []int{0, 1, 2, 3, 4, 5, 10} {
						for _, nrhs := range []int{0, 1, 2, 3, 4, 5, 10, 15} {
							for _, lda := range []int{max(1, n), n + 3} {
								for _, ldb := range []int{max(1, nrhs), nrhs + 3} {
									if diag == blas.Unit {
										dtrtrsTest(t, impl, rnd, uplo, trans, diag, n, nrhs, lda, ldb, false)
									} else {
										dtrtrsTest(t, impl, rnd, uplo, trans, diag, n, nrhs, lda, ldb, true)
										dtrtrsTest(t, impl, rnd, uplo, trans
    
func dtrtrsTest(t *testing.T, impl Dtrtrser, rnd *rand.Rand, uplo blas.Uplo, trans blas.Transpose, diag blas.Diag, n, nrhs int, lda, ldb int, singular bool) {
	if singular && diag == blas.Unit {
		panic("blas.Unit triangular matrix cannot be singular")
	}

	const tol = 1e-14

	if n == 0 {
		singular = false
	}
	name := fmt.Sprintf("uplo=%v,diag=%v,n=%v,nrhs=%v,lda=%v,ldb=%v,sing=%v", string(uplo), string(diag), n, nrhs, lda, ldb, singular)

	// Generate a random triangular matrix A. One of its triangles won't be
	// referenced.
	a := make([]float64, n*lda)
	for i := range a {
		a[i] = rnd.NormFloat64()
	}
	if singular {
		i := rnd.Intn(n)
		a[i*lda+i] = 0
	}
	aCopy := make([]float64, len(a))
	copy(aCopy, a)

	// Generate a random solution matrix X.
	x := make([]float64, n*ldb)
	for i := range x {
		x[i] = rnd.NormFloat64()
	}

	// Generate the right-hand side as A * X  or  Aᵀ * X.
	b := make([]float64, len(x))
	copy(b, x)
	bi := blas64.Implementation()
	bi.Dtrmm(blas.Left, uplo, trans, diag, n, nrhs, 1, a, lda, b, ldb)

	got := make([]float64, len(b))
	copy(got, b)

	ok := impl.Dtrtrs(uplo, trans, diag, n, nrhs, a, lda, got, ldb)

	if !floats.Equal(a, aCopy) {
		t.Errorf("%v: unexpected modification of A", name)
	}

	if ok == singular {
		t.Errorf("%v: misdetected singular matrix, ok=%v", name, ok)
	}

	if !ok {
		if !floats.Equal(got, b) {
			t.Errorf("%v: unexpected modification of B when singular", name)
		}
		return
	}

	if n == 0 || nrhs == 0 {
		return
	}

	work := make([]float64, n)

	// Compute the 1-norm of A or Aᵀ.
	var aNorm float64
	if trans == blas.NoTrans {
		aNorm = dlantr(lapack.MaxColumnSum, uplo, diag, n, n, a, lda, work)
	} else {
		aNorm = dlantr(lapack.MaxRowSum, uplo, diag, n, n, a, lda, work)
	}

	// Compute the maximum over the number of right-hand sides of
	//  |op(A)*x-b| / (|op(A)| * |x|)
	var resid float64
	for j := 0; j < nrhs; j++ {
		bi.Dcopy(n, got[j:], ldb, work, 1)
		bi.Dtrmv(uplo, trans, diag, n, a, lda, work, 1)
		bi.Daxpy(n, -1, b[j:], ldb, work, 1)
		rjNorm := bi.Dasum(n, work, 1)
		xNorm := bi.Dasum(n, got[j:], ldb)
		resid = math.Max(resid, rjNorm/aNorm/xNorm)
	}
	if resid > tol {
		t.Errorf("%v: unexpected result; resid=%v,want<=%v", name, resid, tol)
	}
}