A nice module like File::Spec or Path::Class will probably save you some head-hurt, but here's a possible regex approach (needs 5.10+ for \K):

>perl -wMstrict -le
"my @paths = qw(
   C:\Tools\scripts\Test\Foo.pl
   C:\Tools\Test\Unstable\Foo.pl
   C:\Tools\scripts\Test\Bar.dir\Baz\Foo.pl
   C:\Tools\Test\Baz\Test\Foo.pl
   );
 ;;
 my $all_before_Test = qr{ \A (?: (?! \\ Test) .)* }xms;
 ;;
 for my $path (@paths) {
   print qq{'$path'};
   my @chunks =
     $path =~ m{ (?: $all_before_Test | \G) \\ \K [^\\]+ }xmsg;
   $chunks[-1] =~ s{ [.] [^.]* \z }{}xms;
   my $msg = join q{ - }, @chunks;
   print qq{'$msg' \n};
   }
"
'C:\Tools\scripts\Test\Foo.pl'
'Test - Foo'

'C:\Tools\Test\Unstable\Foo.pl'
'Test - Unstable - Foo'

'C:\Tools\scripts\Test\Bar.dir\Baz\Foo.pl'
'Test - Bar.dir - Baz - Foo'

'C:\Tools\Test\Baz\Test\Foo.pl'
'Test - Baz - Test - Foo'
[download]

If you want 'C:\Tools\Test\Baz\Test\Foo.pl' to render as 'Test - Foo' use
    my $all_before_Test = qr{ \A .* (?= \\ Test) }xms;
instead.