tests: reduce noise on MacOS

This should get rid of

    Openat: O_NOFOLLOW missing: flags = 0x0
    Fchmodat: adding missing AT_SYMLINK_NOFOLLOW flag
    sys_common_test.go:203: chmod on symlink should have failed, but did not. New mode=0333
    UnmountErr: "[...]/057376762.mnt" was not found in MountInfo, cannot check for FD leak

and add some context to

    --- FAIL: TestUtimesNano (0.00s)
    matrix_test.go:628: no such file or directory

See https://github.com/rfjakob/gocryptfs/pull/343#issuecomment-453888006
for full test output

3 files changed, 13 insertions, 7 deletions

diff --git a/internal/syscallcompat/sys_common_test.go b/internal/syscallcompat/sys_common_test.go
index 3e2d80e..bbb6dbc 100644
--- a/internal/syscallcompat/sys_common_test.go
+++ b/internal/syscallcompat/sys_common_test.go
@@ -38,7 +38,9 @@ func TestReadlinkat(t *testing.T) {
 }
 
 func TestOpenat(t *testing.T) {
-	_, err := Openat(tmpDirFd, "testOpenAt", 0, 0)
+	// Always pass O_NOFOLLOW to avoid this warning:
+	// Openat: O_NOFOLLOW missing: flags = 0x0"
+	_, err := Openat(tmpDirFd, "testOpenAt", syscall.O_NOFOLLOW, 0)
 	if err == nil {
 		t.Errorf("should have failed")
 	}
@@ -47,7 +49,7 @@ func TestOpenat(t *testing.T) {
 		t.Fatal(err)
 	}
 	fd.Close()
-	rawFd, err := Openat(tmpDirFd, "testOpenAt", 0, 0)
+	rawFd, err := Openat(tmpDirFd, "testOpenAt", syscall.O_NOFOLLOW, 0)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -56,7 +58,7 @@ func TestOpenat(t *testing.T) {
 		t.Fatalf("rawFd=%d", rawFd)
 	}
 	// Test with absolute path
-	rawFd, err = Openat(-1, tmpDir+"/testOpenAt", 0, 0)
+	rawFd, err = Openat(-1, tmpDir+"/testOpenAt", syscall.O_NOFOLLOW, 0)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -156,7 +158,7 @@ func TestUnlinkat(t *testing.T) {
 	}
 }
 
-func TestFchmodat(t *testing.T) {
+func TestFchmodatNofollow(t *testing.T) {
 	regular := "TestFchmodat_Regular"
 	f, err := os.OpenFile(tmpDir+"/"+regular, os.O_CREATE|os.O_WRONLY, 0000)
 	if err != nil {
@@ -197,7 +199,10 @@ func TestFchmodat(t *testing.T) {
 
 	// Check what happens on a symlink
 	err = FchmodatNofollow(dirfd, symlink, 0333)
-	if err == nil {
+	// On Darwin, permissions on symlinks are significant and can be changed. On
+	// Linux they are ignored, and FchmodatNofollow rejects attempts to change
+	// them.
+	if err == nil && runtime.GOOS == "linux" {
 		syscall.Lstat(tmpDir+"/"+symlink, &st)
 		st.Mode &= 0777
 		t.Errorf("chmod on symlink should have failed, but did not. New mode=%#0o", st.Mode)
diff --git a/tests/matrix/matrix_test.go b/tests/matrix/matrix_test.go
index ad2eeae..e4c6b5f 100644
--- a/tests/matrix/matrix_test.go
+++ b/tests/matrix/matrix_test.go
@@ -625,7 +625,7 @@ func doTestUtimesNano(t *testing.T, path string) {
 	for i, tc := range utimeTestcases {
 		err := syscall.UtimesNano(path, tc.in[:])
 		if err != nil {
-			t.Fatal(err)
+			t.Fatalf("%q: %v", path, err)
 		}
 		var st syscall.Stat_t
 		err = syscall.Stat(path, &st)
diff --git a/tests/test_helpers/mount_unmount.go b/tests/test_helpers/mount_unmount.go
index 1d43418..20b1143 100644
--- a/tests/test_helpers/mount_unmount.go
+++ b/tests/test_helpers/mount_unmount.go
@@ -133,7 +133,8 @@ func UnmountErr(dir string) (err error) {
 	var fdsNow []string
 	pid := MountInfo[dir].Pid
 	fds := MountInfo[dir].Fds
-	if pid <= 0 {
+	if pid <= 0 && runtime.GOOS == "linux" {
+		// The FD leak check only works on Linux.
 		fmt.Printf("UnmountErr: %q was not found in MountInfo, cannot check for FD leaks\n", dir)
 	}