testing: revert GOTMPDIR hack for setting testscript workdir root (#673)

In 854efae we included a temporary hack for setting the destination of
artefacts for testscript tests, via GOTMPDIR. In this commit we undo
that hack.

Motivation for the change best described in:

rogpeppe/go-internal@bc89b17

cmd/govim/main_test.go

@@ -47,16 +47,10 @@ func TestMain(m *testing.M) {
 }
 
 func TestScripts(t *testing.T) {
-	// TODO our approach with setting the workdir root via os.Setenv("GOTMPDIR")
-	// is hacky and gross. Working out a cleaner approach with rogpeppe, likely
-	// passing in such a value via Params
+	t.Parallel()
 	var workdir string
-	if envworkdir := os.Getenv(testsetup.EnvTestscriptWorkdirRoot); envworkdir == "" {
-		// i.e. we are not going to call os.Setenv below
-		t.Parallel()
-	} else {
+	if envworkdir := os.Getenv(testsetup.EnvTestscriptWorkdirRoot); envworkdir != "" {
 		workdir = filepath.Join(envworkdir, "cmd", "govim"+raceOrNot())
-		defer os.Setenv("GOTMPDIR", os.Getenv("GOTMPDIR"))
 	}
 
 	var waitLock sync.Mutex
@@ -92,14 +86,11 @@ func TestScripts(t *testing.T) {
 		if workdir != "" {
 			workdir = filepath.Join(workdir, entry.Name())
 			os.MkdirAll(workdir, 0777)
-			os.Setenv("GOTMPDIR", workdir)
 		}
 		t.Run(entry.Name(), func(t *testing.T) {
-			// Do not call t.Parallel here. We currently rely on this being
-			// run on the test goroutine in order that os.Setenv is not racey
 			params := testscript.Params{
-				TestWork: workdir != "",
-				Dir:      filepath.Join("testdata", entry.Name()),
+				WorkdirRoot: workdir,
+				Dir:         filepath.Join("testdata", entry.Name()),
 				Cmds: map[string]func(ts *testscript.TestScript, neg bool, args []string){
 					"sleep":       testdriver.Sleep,
 					"errlogmatch": testdriver.ErrLogMatch,

go.mod

@@ -9,7 +9,7 @@ require (
 	github.com/fsnotify/fsnotify v1.4.7
 	github.com/kr/pretty v0.1.0
 	github.com/myitcv/vbash v0.0.4
-	github.com/rogpeppe/go-internal v1.5.1
+	github.com/rogpeppe/go-internal v1.5.2
 	golang.org/x/mod v0.1.1-0.20191105210325-c90efee705ee
 	golang.org/x/sync v0.0.0-20190423024810-112230192c58
 	golang.org/x/sys v0.0.0-20190429190828-d89cdac9e872 // indirect

go.sum

@@ -33,8 +33,8 @@ github.com/rogpeppe/clock v0.0.0-20190514195947-2896927a307a h1:3QH7VyOaaiUHNrA9
 github.com/rogpeppe/clock v0.0.0-20190514195947-2896927a307a/go.mod h1:4r5QyqhjIWCcK8DO4KMclc5Iknq5qVBAlbYYzAbUScQ=
 github.com/rogpeppe/go-internal v1.2.1/go.mod h1:M8bDsm7K2OlrFYOpmOWEs/qY81heoFRclV5y23lUDJ4=
 github.com/rogpeppe/go-internal v1.3.0/go.mod h1:M8bDsm7K2OlrFYOpmOWEs/qY81heoFRclV5y23lUDJ4=
-github.com/rogpeppe/go-internal v1.5.1 h1:asQ0uD7BN9RU5Im41SEEZTwCi/zAXdMOLS3npYaos2g=
-github.com/rogpeppe/go-internal v1.5.1/go.mod h1:xXDCJY+GAPziupqXw64V24skbSoqbTEfhy4qGm1nDQc=
+github.com/rogpeppe/go-internal v1.5.2 h1:qLvObTrvO/XRCqmkKxUlOBc48bI3efyDuAZe25QiF0w=
+github.com/rogpeppe/go-internal v1.5.2/go.mod h1:xXDCJY+GAPziupqXw64V24skbSoqbTEfhy4qGm1nDQc=
 github.com/sergi/go-diff v1.0.0 h1:Kpca3qRNrduNnOQeazBd0ysaKrUJiIuISHxogkT9RPQ=
 github.com/sergi/go-diff v1.0.0/go.mod h1:0CfEIISq7TuYL3j771MWULgwwjU+GofnZX9QAmXWZgo=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=

govim_test.go

@@ -35,26 +35,16 @@ func TestMain(m *testing.M) {
 }
 
 func TestScripts(t *testing.T) {
-	// TODO our approach with setting the workdir root via os.Setenv("GOTMPDIR")
-	// is hacky and gross. Working out a cleaner approach with rogpeppe, likely
-	// passing in such a value via Params
+	t.Parallel()
 	workdir := os.Getenv(testsetup.EnvTestscriptWorkdirRoot)
-	if workdir == "" {
-		// i.e. we are not going to call os.Setenv below
-		t.Parallel()
-	} else {
-		os.MkdirAll(workdir, 0777)
-		os.Setenv("GOTMPDIR", workdir)
-		defer os.Setenv("GOTMPDIR", os.Getenv("GOTMPDIR"))
-	}
 
 	var waitLock sync.Mutex
 	var waitList []func() error
 
 	t.Run("scripts", func(t *testing.T) {
 		testscript.Run(t, testscript.Params{
-			TestWork: workdir != "",
-			Dir:      "testdata",
+			WorkdirRoot: workdir,
+			Dir:         "testdata",
 			Cmds: map[string]func(ts *testscript.TestScript, neg bool, args []string){
 				"sleep":       testdriver.Sleep,
 				"errlogmatch": testdriver.ErrLogMatch,