[6.d] Spec start in sink context attaches ex. handler

POV: rakudo/rakudo@6ee5f75778
Per 6.d-prep: https://github.com/perl6/6.d-prep/blob/69a7d9c5e5d8ff3bed69c6f33577ada4bb8470be/TODO/FEATURES.md#make-start-blocks-in-sink-context-attach-an-error-handler

MISC/misc-6.d.t

@@ -7,7 +7,7 @@ use Test::Util;
 # They might be rearranged into other files in the future, but for now, keeping them in this
 # file avoids creating a ton of `-6.d.t` files for the sake of single tests.
 
-plan 6;
+plan 7;
 
 group-of 6 => ':sym<> colonpair on subroutine names is reserved' => {
     throws-like 'use v6.d.PREVIEW; sub meow:sym<bar> {}', X::Syntax::Reserved, ':sym<...>';
@@ -196,4 +196,45 @@ group-of 3 => 'smiley constraints default to type object without smiley' => {
     }
 }
 
+group-of 6 => 'sunk `start`' => {
+    is_run ｢
+      use v6.d.PREVIEW;
+      start { die "PASS" }; sleep ⅓; print "fail"
+    ｣, {:out{not .contains: 'fail'}, :err{.contains: 'PASS'}, :1status }, 'block';
+
+    is_run ｢
+      use v6.d.PREVIEW;
+      start die "PASS"; sleep ⅓; print "pass"
+    ｣, {:out{not .contains: 'fail'}, :err{.contains: 'PASS'}, :1status }, 'thunk';
+
+    is_run ｢
+      use v6.d.PREVIEW;
+      start { CATCH { when X::Str::Numeric {} }; die "PASS" };
+      sleep ⅓; print "pass"
+    ｣, {:out{not .contains: 'fail'}, :err{.contains: 'PASS'}, :1status },
+      'with non-catching handler';
+
+    is_run ｢
+      use v6.d.PREVIEW;
+      start { CATCH { default { note "caught" } }; die "PASS" }
+      sleep ⅓; print "pass"
+    ｣, {:out<pass>, :err{.contains: 'caught'}, :0status },
+      'with catching handler';
+
+    is_run ｢
+      use v6.d.PREVIEW;
+      (start die "fail"; sleep ⅓).sink;
+      print "pass"
+    ｣, {:out{not .contains: 'fail'}, :err{not .contains: 'PASS'}, :0status },
+      'non-sunk context, even if we call .sink on it';
+
+    is_run ｢
+      use v6.d.PREVIEW;
+      class Exceptions::Meows { method process (| --> False) { note "MEOWS" } }
+      BEGIN %*ENV<PERL6_EXCEPTIONS_HANDLER> = 'Meows';
+      start die "PASS"; sleep ⅓; print "fail"
+    ｣, {:out{not .contains: 'fail'}, :err{.contains: 'MEOWS'}, :1status},
+        'custom exceptions handler respected';
+}
+
 # vim: expandtab shiftwidth=4 ft=perl6