$VAR1 = {                                  
          'block1' => {
                        'lib1' => {
                                    'cell_1' => 1,
                                    'cell_2' => 1,
                                  },
                      },
          'block2' => {
                        'lib1' => {
                                    'cell_3' => 1,
                                    'cell_4' => 1,
                                  },
                      },
        };

##</code><code>##

if(!defined $hash_ref->{$block}->{$libName}) {
             print "This is a test\n";
}

##</code><code>##

$VAR1 = {
          'block1' => {
                        'lib1' => {
                                    'cell_1' => 1,
                                    'cell_2' => 1,
                                  },
                      },
          'block2' => {
                        'lib1' => {
                                    'cell_3' => 1,
                                    'cell_4' => 1,
                                  },
                      },
          'block3' => {},
        };