improve GOOS=tamago test coverage

src/os/os_test.go

@@ -1453,7 +1453,7 @@ func testChtimesOmit(t *testing.T, omitAt, omitMt bool) {
 	if !gotAtime.Equal(wantAtime) {
 		errormsg := fmt.Sprintf("atime mismatch, got: %q, want: %q", gotAtime, wantAtime)
 		switch runtime.GOOS {
-		case "plan9":
+		case "plan9", "tamago":
 			// Mtime is the time of the last change of content.
 			// Similarly, atime is set whenever the contents are
 			// accessed; also, it is set whenever mtime is set.
@@ -1531,7 +1531,7 @@ func testChtimes(t *testing.T, name string) {
 	if !pat.Before(at) {
 		errormsg := fmt.Sprintf("AccessTime didn't go backwards; was=%v, after=%v", at, pat)
 		switch runtime.GOOS {
-		case "plan9":
+		case "plan9", "tamago":
 			// Mtime is the time of the last change of
 			// content.  Similarly, atime is set whenever
 			// the contents are accessed; also, it is set

src/os/read_test.go

@@ -72,7 +72,7 @@ func TestReadOnlyWriteFile(t *testing.T) {
 	if Getuid() == 0 {
 		t.Skipf("Root can write to read-only files anyway, so skip the read-only test.")
 	}
-	if runtime.GOOS == "wasip1" {
+	if runtime.GOOS == "wasip1" || runtime.GOOS == "tamago" {
 		t.Skip("no support for file permissions on " + runtime.GOOS)
 	}
 	t.Parallel()

src/os/removeall_test.go

@@ -273,7 +273,7 @@ func TestRemoveReadOnlyDir(t *testing.T) {
 // Issue #29983.
 func TestRemoveAllButReadOnlyAndPathError(t *testing.T) {
 	switch runtime.GOOS {
-	case "js", "wasip1", "windows":
+	case "js", "wasip1", "windows", "tamago":
 		t.Skipf("skipping test on %s", runtime.GOOS)
 	}
 
@@ -421,7 +421,7 @@ func TestRemoveAllWithMoreErrorThanReqSize(t *testing.T) {
 		return
 	}
 	if err == nil {
-		if runtime.GOOS == "windows" || runtime.GOOS == "wasip1" {
+		if runtime.GOOS == "windows" || runtime.GOOS == "wasip1" || runtime.GOOS == "tamago" {
 			// Marking a directory as read-only in Windows does not prevent the RemoveAll
 			// from creating or removing files within it.
 			//

src/os/testdata_tamago_test.go

@@ -1,10 +1,23 @@
 //go:build tamago
-package os
+package os_test
 
 import (
 	"embed"
+	"os"
+	"syscall"
 )
 
+//go:embed *.go exec/*
+var src embed.FS
+
 //go:embed testdata/*
 var testdata embed.FS
-func init() { CopyFS(".", testdata) }
+
+func init() {
+	// cwd in TestDirFSRootDir must not be empty
+	os.MkdirAll("./1", 0777)
+	syscall.Chdir("./1")
+
+	os.CopyFS(".", src)
+	os.CopyFS(".", testdata)
+}