os/user: skip tests that invoke Current if it returns an expected error

Today Current may fail if the binary is not built with cgo
and USER and/or HOME is not set in the environment.
That should not cause the test to fail.

After this change,

	GOCACHE=$(go env GOCACHE) CGO_ENABLED=0 USER= HOME= go test os/user

now passes on linux/amd64.

For #59583.

Change-Id: Id290cd1088051e930d73f0dd554177124796e8f2
Reviewed-on: https://go-review.googlesource.com/c/go/+/487015
Reviewed-by: Michael Pratt <mpratt@google.com>
Run-TryBot: Bryan Mills <bcmills@google.com>
Reviewed-by: Johan Brandhorst-Satzkorn <johan.brandhorst@gmail.com>
Auto-Submit: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

src/os/user/cgo_user_test.go

@@ -0,0 +1,11 @@
+// Copyright 2023 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.
+
+//go:build cgo && !osusergo
+
+package user
+
+func init() {
+	hasCgo = true
+}

src/os/user/user_test.go

@@ -5,9 +5,16 @@
 package user
 
 import (
+	"os"
 	"testing"
 )
 
+var (
+	hasCgo  = false
+	hasUSER = os.Getenv("USER") != ""
+	hasHOME = os.Getenv("HOME") != ""
+)
+
 func checkUser(t *testing.T) {
 	t.Helper()
 	if !userImplemented {
@@ -23,7 +30,11 @@ func TestCurrent(t *testing.T) {
 	userBuffer = 1 // force use of retry code
 	u, err := Current()
 	if err != nil {
+		if hasCgo || (hasUSER && hasHOME) {
 			t.Fatalf("Current: %v (got %#v)", err, u)
+		} else {
+			t.Skipf("skipping: %v", err)
+		}
 	}
 	if u.HomeDir == "" {
 		t.Errorf("didn't get a HomeDir")
@@ -62,8 +73,13 @@ func TestLookup(t *testing.T) {
 
 	want, err := Current()
 	if err != nil {
+		if hasCgo || (hasUSER && hasHOME) {
 			t.Fatalf("Current: %v", err)
+		} else {
+			t.Skipf("skipping: %v", err)
 		}
+	}
+
 	// TODO: Lookup() has a fast path that calls Current() and returns if the
 	// usernames match, so this test does not exercise very much. It would be
 	// good to try and test finding a different user than the current user.
@@ -79,8 +95,13 @@ func TestLookupId(t *testing.T) {
 
 	want, err := Current()
 	if err != nil {
+		if hasCgo || (hasUSER && hasHOME) {
 			t.Fatalf("Current: %v", err)
+		} else {
+			t.Skipf("skipping: %v", err)
 		}
+	}
+
 	got, err := LookupId(want.Uid)
 	if err != nil {
 		t.Fatalf("LookupId: %v", err)
@@ -102,9 +123,14 @@ func TestLookupGroup(t *testing.T) {
 	}()
 	groupBuffer = 1 // force use of retry code
 	checkGroup(t)
+
 	user, err := Current()
 	if err != nil {
-		t.Fatalf("Current(): %v", err)
+		if hasCgo || (hasUSER && hasHOME) {
+			t.Fatalf("Current: %v", err)
+		} else {
+			t.Skipf("skipping: %v", err)
+		}
 	}
 
 	g1, err := LookupGroupId(user.Gid)
@@ -137,10 +163,16 @@ func checkGroupList(t *testing.T) {
 
 func TestGroupIds(t *testing.T) {
 	checkGroupList(t)
+
 	user, err := Current()
 	if err != nil {
-		t.Fatalf("Current(): %v", err)
+		if hasCgo || (hasUSER && hasHOME) {
+			t.Fatalf("Current: %v", err)
+		} else {
+			t.Skipf("skipping: %v", err)
 		}
+	}
+
 	gids, err := user.GroupIds()
 	if err != nil {
 		t.Fatalf("%+v.GroupIds(): %v", user, err)