cmd/go: convert one test from test.bash to Go

Sending out the conversion of a single test to get comments on the
overall approach.  Converting more tests will follow.

Change-Id: I4755442d08aeb6f74c46856ae406fec41cf8d5dc
Reviewed-on: https://go-review.googlesource.com/10464
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

src/cmd/go/go_test.go

+// Copyright 2015 The Go 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 main_test
+
+import (
+	"bytes"
+	"flag"
+	"fmt"
+	"io/ioutil"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"runtime"
+	"strings"
+	"testing"
+)
+
+// Whether we can run go or ./testgo.
+var canRun = true
+
+func init() {
+	switch runtime.GOOS {
+	case "android", "nacl":
+		canRun = false
+	case "darwin":
+		switch runtime.GOARCH {
+		case "arm", "arm64":
+			canRun = false
+		}
+	}
+}
+
+// The TestMain function creates a go command for testing purposes and
+// deletes it after the tests have been run.
+func TestMain(m *testing.M) {
+	flag.Parse()
+
+	if canRun {
+		// We give the executable a .exe extension because Windows.
+		out, err := exec.Command("go", "build", "-tags", "testgo", "-o", "testgo.exe").CombinedOutput()
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "building testgo failed: %v\n%s", err, out)
+			os.Exit(2)
+		}
+	}
+
+	// Don't let these environment variables confuse the test.
+	os.Unsetenv("GOBIN")
+	os.Unsetenv("GOPATH")
+	os.Unsetenv("GOROOT")
+
+	r := m.Run()
+
+	if canRun {
+		os.Remove("testgo.exe")
+	}
+
+	os.Exit(r)
+}
+
+// Skip a test if we can't run ./testgo.
+func checkTestGo(t *testing.T) {
+	if !canRun {
+		switch runtime.GOOS {
+		case "android", "nacl":
+			t.Skipf("skipping on %s", runtime.GOOS)
+		case "darwin":
+			switch runtime.GOARCH {
+			case "arm", "arm64":
+				t.Skipf("skipping on %s/%s, no fork", runtime.GOOS, runtime.GOARCH)
+			}
+		default:
+			t.Skip("skipping for unknown reason")
+		}
+	}
+}
+
+// runTestGo runs the test go command, returning stdout, stderr, and
+// status.  The contents of addEnv are added to the environment.
+func runTestGo(addEnv []string, args ...string) (stdout, stderr string, err error) {
+	if !canRun {
+		panic("runTestGo called but canRun false")
+	}
+
+	cmd := exec.Command("./testgo.exe", args...)
+	var ob, eb bytes.Buffer
+	cmd.Stdout = &ob
+	cmd.Stderr = &eb
+	if len(addEnv) > 0 {
+		cmd.Env = append(addEnv, os.Environ()...)
+	}
+	err = cmd.Run()
+	return ob.String(), eb.String(), err
+}
+
+// tempFile describes a file to put into a temporary directory.
+type tempFile struct {
+	path     string
+	contents string
+}
+
+// tempDir describes a temporary directory created for a single test.
+type tempDir struct {
+	name string
+}
+
+// makeTempDir creates a temporary directory for a single test.
+func makeTempDir(t *testing.T, files []tempFile) *tempDir {
+	dir, err := ioutil.TempDir("", "gotest")
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, f := range files {
+		if err := ioutil.WriteFile(filepath.Join(dir, f.path), []byte(f.contents), 0666); err != nil {
+			t.Fatal(err)
+		}
+	}
+	return &tempDir{dir}
+}
+
+// path returns the absolute pathname to file within tempDir.
+func (td *tempDir) path(name string) string {
+	return filepath.Join(td.name, name)
+}
+
+// Remove a temporary directory after a test completes.  This is
+// normally called via defer.
+func (td *tempDir) remove(t *testing.T) {
+	if err := os.RemoveAll(td.name); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+	}
+}
+
+func TestFileLineInErrorMessages(t *testing.T) {
+	checkTestGo(t)
+	td := makeTempDir(t, []tempFile{{"err.go", `package main; import "bar"`}})
+	defer td.remove(t)
+	path := td.path("err.go")
+	stdout, stderr, err := runTestGo(nil, "run", path)
+	if err == nil {
+		t.Fatal("go command did not fail")
+	}
+	lines := strings.Split(stderr, "\n")
+	for _, ln := range lines {
+		if strings.HasPrefix(ln, path+":") {
+			// Test has passed.
+			return
+		}
+	}
+	t.Log(err)
+	t.Log(stdout)
+	t.Log(stderr)
+	t.Error("missing file:line in error message")
+}

src/cmd/go/test.bash

@@ -45,21 +45,6 @@ unset GOBIN
 unset GOPATH
 unset GOROOT
 
-TEST 'file:line in error messages'
-# Test that error messages have file:line information at beginning of
-# the line. Also test issue 4917: that the error is on stderr.
-d=$(TMPDIR=/var/tmp mktemp -d -t testgoXXX)
-fn=$d/err.go
-echo "package main" > $fn
-echo 'import "bar"' >> $fn
-./testgo run $fn 2>$d/err.out || true
-if ! grep -q "^$fn:" $d/err.out; then
-	echo "missing file:line in error message"
-	cat $d/err.out
-	ok=false
-fi
-rm -r $d
-
 TEST 'program name in crash messages'
 linker=$(./testgo env GOCHAR)l
 d=$(TMPDIR=/var/tmp mktemp -d -t testgoXXX)