Or just:

    use Test::More;
    open my $foo, "<", "somefile.txt" or die;
    () = <$foo>;
    plan tests => 10 + $.;
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And if your tests aren't going to run on systems that don't have wc:

    {no warnings;
     use Test::More plan => 10 + `wc -l "somefile.txt"`}
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