"for $my os (values %info) {"

Two corrections:

• Typo: $my os should be my $os
• Datatype: %info should be %$info (to match OP's $info->{$os}...)

 

"This should also work if you have several errors possible for one testcase, such as 'error1', 'error2', etc."

You're manufacturing data that the OP hasn't specified or even hinted at. I don't think this is a good idea. Furthermore, you're not targeting the specific key (i.e. error) that the OP did specify; you are, in fact, targeting every key that exists. Consider this scenario (using your code, with the corrections shown above):

$ perl -Mstrict -Mwarnings -le '
    my $info = {
        win => {
            t1 => { error => "missing arg" },
            t2 => { skipped => "no network" }
        },
        nix => {
            t1 => { error => "wrong type" },
            t2 => { success => 1 }
        }
    };

    my @errors;

    for my $os (values %$info) {
        for my $testcase (values %$os) {
            push @errors, values %$testcase
        }
    }

    print for @errors;
'
no network
missing arg
wrong type
1
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