Test for deprecation warning

Author: zmughal

t/basic.t

@@ -3,6 +3,7 @@
 use Data::Frame::Setup;
 
 use Test2::V0;
+use Test2::Tools::Warnings qw/warning/;
 
 use Data::Frame;
 use PDL::Core qw(pdl);
@@ -33,7 +34,15 @@ is( $df_array->column_names, [ qw/z y x/ ] );
 is( $df_hash->column_names, [ qw/a b c/ ] );
 
 is( $df_hash->column('c')->length, 4);
-is( $df_hash->column('c')->number_of_rows, 4);
+{
+	my $length;
+	like(
+		warning { $length = $df_hash->column('c')->number_of_rows },
+		qr/deprecated/,
+		'Got deprecation warning'
+	);
+	is($length , 4);
+}
 is( $df_hash->column('c')->unpdl, $c);
 
 like(