Modernise & improve SelectSaver.t coverage

 - Use v5.40 and a modern testing framework.
 - Test different arguments to new.
 - Avoid writing to disk, it isn't necessary.

Author: JRaspass

lib/SelectSaver.t

@@ -5,24 +5,63 @@ BEGIN {
     @INC = '../lib';
 }
 
-print "1..3\n";
+use v5.40;
 
-use SelectSaver;
+use Test2::V0 -target => 'SelectSaver';
 
-open(FOO, ">", "foo-$$") || die;
+ok dies { SelectSaver::new() }, 'Too few arguments to new dies';
+ok dies { CLASS->new(undef, undef) }, 'Too many arguments to new dies';
 
-print "ok 1\n";
-{
-    my $saver = new SelectSaver(FOO);
-    print "foo\n";
-}
+subtest 'bareword filehandle' => sub {
+    use feature 'bareword_filehandles';
+
+    is refaddr(select), refaddr(*STDOUT), 'STDOUT is initially selected';
+
+    open FOO, '>', undef;
+
+    {
+        ok my $saver = CLASS->new(*FOO), 'SelectSaver->new(*FOO)';
+
+        is refaddr(select), refaddr(*FOO), 'FOO is now selected';
+    }
+
+    is refaddr(select), refaddr(*STDOUT), 'STDOUT is selected again';
+
+    {
+        ok my $saver = CLASS->new('FOO'), 'SelectSaver->new("FOO")';
+
+        is refaddr(select), refaddr(*FOO), 'FOO is now selected';
+    }
+
+    is refaddr(select), refaddr(*STDOUT), 'STDOUT is selected again';
+};
+
+subtest 'lexical filehandle' => sub {
+    is refaddr(select), refaddr(*STDOUT), 'STDOUT is initially selected';
+
+    open my $fh, '>', undef;
+
+    {
+        ok my $saver = CLASS->new($fh), 'SelectSaver->new($fh)';
+
+        is refaddr(select), refaddr($fh), '$fh is now selected';
+    }
+
+    is refaddr(select), refaddr(*STDOUT), 'STDOUT is selected again';
+};
+
+subtest 'no filehandle' => sub {
+    is refaddr(select), refaddr(*STDOUT), 'STDOUT is initially selected';
+
+    {
+        ok my $saver = CLASS->new, 'SelectSaver->new';
+
+        ok select(STDERR), 'select STDERR';
 
-# Get data written to file
-open(FOO, "<", "foo-$$") || die;
-chomp($foo = <FOO>);
-close FOO;
-unlink "foo-$$";
+        is refaddr(select), refaddr(*STDERR), 'STDERR is now selected';
+    }
 
-print "ok 2\n" if $foo eq "foo";
+    is refaddr(select), refaddr(*STDOUT), 'STDOUT is selected again';
+};
 
-print "ok 3\n";
+done_testing;