{
    my $warning;
    local $SIG{__WARN__} = sub { $warning = shift; };
    Module::do_something($param, $param1);
    like ($warning, qr/ignoring/, 'param 1 isn't an href, ignored');
}

##</code><code>##

sub blah {
    my %params = @_;
    ...
}

##</code><code>##

my $farm = blah(moo => $href, meow => "Phoebe's smelly cat");

##</code><code>##

sub valid_params {
    my %valid = (
        moo => 1,
        woof => 1,
        meow => 1,
    );
    return %valid;
}
sub _validate_params {
    my %p = @_;
    
    my %valid = valid_params();

    for (keys %p){
        die "$_ isn't a valid param" if ! exists $valid{$_};
    }
    if (exists $p{moo} && ref $p{moo} ne 'HASH'){
        die "param 'moo' must be a hash reference";
    }
}

##</code><code>##

sub yell {
    my %p = @_;
    _validate_params(%p);
    ...
}