Define minimal preamble instead of skipping compilation test

Author: coke

doc/Language/typesystem.pod6

@@ -782,14 +782,14 @@ Returns the list of enum-pairs. Works both on the enum type and any key.
 
 Returns the key of an enum-pair.
 
-=for code :skip-test
+=for code :preamble<<enum Mass<g> >>
 say g.key; # OUTPUT: «g␤»
 
 =head4 method value
 
 Returns the value of an enum-pair.
 
-=for code :skip-test
+=for code :preamble<<enum Mass<g> >>
 say g.value; # OUTPUT: «1␤»
 
 =head4 method pair
@@ -801,7 +801,7 @@ method pair(::?CLASS:D:)
 
 Returns a C<Pair> of the enum-pair.
 
-=for code :skip-test
+=for code :preamble<<enum Mass<g> >>
 say g.pair; # OUTPUT: «g => 1␤»
 
 =head4 method kv
@@ -813,7 +813,7 @@ multi method kv(::?CLASS:D:)
 
 Returns a list with key and value of the enum-pair.
 
-=for code :skip-test
+=for code :preamble<<enum Mass<g> >>
 say g.kv; # OUTPUT: «(g 1)␤»
 
 =head3 Coercion