}
	if len(args) == 0 {
		t.Skip("no C++ compiler")
	}
	testenv.MustHaveExecPath(t, string(args[0]))
}

var (
	swigOnce sync.Once
	haveSwig bool
)

func mustHaveSwig(t *testing.T) {
	swigOnce.Do(func() {
		mustHaveSwigOnce(t)
		haveSwig = true
	})
	// The first call will skip t with a nice message. On later calls, we just skip.
	if !haveSwig {
		t.Skip("swig not found")
	}
}

As a simple example, consider a package that uses cgo to call C.sin.
The following code will be generated by cgo:

	// compiled by gc

	//go:cgo_ldflag "-lm"

	type _Ctype_double float64

	//go:cgo_import_static _cgo_gcc_Cfunc_sin
	//go:linkname __cgo_gcc_Cfunc_sin _cgo_gcc_Cfunc_sin
	var __cgo_gcc_Cfunc_sin byte
	var _cgo_gcc_Cfunc_sin = unsafe.Pointer(&__cgo_gcc_Cfunc_sin)

		}()
	}
	wg.Wait()
})

func TestIssue21181(t *testing.T) {
	if testing.Short() {
		t.Skip("skipping with -short")
	}
	if *flagCheck {
		// slow, not worth repeating in -check
		t.Skip("skipping with -check set")
	}
	testenv.MustHaveGoBuild(t)

	warmupCache()

	for _, context := range contexts {

package cgotest

import (
	"bytes"
	"crypto/md5"
	"os"
	"os/exec"
	"runtime"
	"syscall"
	"testing"
	"time"
)

func test18146(t *testing.T) {
	if testing.Short() {
		t.Skip("skipping in short mode")
	}

	if runtime.GOOS == "darwin" || runtime.GOOS == "ios" {
		t.Skipf("skipping flaky test on %s; see golang.org/issue/18202", runtime.GOOS)
	}

<code>package math</code>, which exports function <code>Sin</code>, and
installed the compiled package in the file identified by
<code>"lib/math"</code>.
This table illustrates how <code>Sin</code> is accessed in files
that import the package after the
various types of import declaration.
</p>

<pre class="grammar">
Import declaration          Local name of Sin

import   "lib/math"         math.Sin

// Test that the stack can be unwound through a call out and call back
// into Go.
func testCallbackCallers(t *testing.T) {
	if runtime.Compiler != "gc" {
		// The exact function names are not going to be the same.
		t.Skip("skipping for non-gc toolchain")
	}
	pc := make([]uintptr, 100)
	n := 0
	name := []string{
		"runtime.cgocallbackg1",
		"runtime.cgocallbackg",
		"runtime.cgocallback",
		"runtime.systemstack_switch",

		// implementation of a no-network check using 'unshare -n -r'.
		// Since this test does need root to work, we need to skip it.
		t.Skip("skipping root only test on a non-root builder")
	}
	if runtime.GOOS == "linux" {
		if _, err := os.Stat("/etc/alpine-release"); err == nil {
			t.Skip("skipping failing test on alpine - go.dev/issue/19938")
		}
	}

	// Launch some threads in C.
	const cts = 5
	C.trial(cts)

// one.

import (
	"bytes"
	"debug/elf"
	"os"
	"testing"
)

func testBuildID(t *testing.T) {
	f, err := elf.Open("/proc/self/exe")
	if err != nil {
		if os.IsNotExist(err) {
			t.Skip("no /proc/self/exe")
		}
		t.Fatal("opening /proc/self/exe: ", err)
	}
	defer f.Close()

	c := 0
sections:
	for i, s := range f.Sections {
		if s.Type != elf.SHT_NOTE {
			continue
		}

func NewTokenizer(name string, r io.Reader, file *os.File) *Tokenizer {
	var s scanner.Scanner
	s.Init(r)
	// Newline is like a semicolon; other space characters are fine.
	s.Whitespace = 1<<'\t' | 1<<'\r' | 1<<' '
	// Don't skip comments: we need to count newlines.
	s.Mode = scanner.ScanChars |
		scanner.ScanFloats |
		scanner.ScanIdents |
		scanner.ScanInts |
		scanner.ScanStrings |
		scanner.ScanComments
	s.Position.Filename = name

		return
	}

	f.formatOctal(b, 0) // Last resort, just write zero
	f.err = ErrFieldTooLong
}

func (p *parser) parseOctal(b []byte) int64 {
	// Because unused fields are filled with NULs, we need
	// to skip leading NULs. Fields may also be padded with
	// spaces or NULs.
	// So we remove leading and trailing NULs and spaces to
	// be sure.
	b = bytes.Trim(b, " \x00")

	if len(b) == 0 {
		return 0
	}