https://github.com/azawawi/perl6-gtk-simpler/blob/master/examples/17-scrolled-window-with-textview.p6

$ raku -v
This is Rakudo version 2020.05.1 built on MoarVM version 2020.05
implementing Raku 6.d.

$ gtk-scrolled-window-with-textview.p6
No such symbol 'GTK::Simple::TextView'
in sub text-view at /opt/rakudo-pkg/share/perl6/site/sources/4838F43F2EF3891FE757A014B4DDF064B47D541A (GTK::Simpler) line 230
in block at ./gtk-scrolled-window-with-textview.p6 line 8

8: my $send-history = text-view(text=>'Old stuff');

I tried to install GTK::Simpler.
It runs the sanity test and a window indeed appears but if fails nevertheless

$ zef install GTK::Simpler
===> Searching for: GTK::Simpler
===> Testing: GTK::Simpler:ver<0.0.5>

Failed test at t/01-sanity.t line 11

Failed

Looks like you failed 1 test of 3

===> Testing [FAIL]: GTK::Simpler:ver<0.0.5>
Aborting due to test failure: GTK::Simpler:ver<0.0.5> (use --force-test to override)

This is Rakudo version 2018.06-225-ge9e8cd550 built on MoarVM version 2018.06-262-g0b08d3c18