Add ignoremark regex tests for when there are Prepend cp's

Test to make sure that we match the correct base codepoint when we
have Prepend characters. If we have all Prepend and no base or Prepend
+ Extend only, then match the first codepoint instead.

S05-modifier/ignoremark.t

@@ -1,7 +1,7 @@
 use v6;
 use Test;
 
-plan 36;
+plan 43;
 
 =begin description
 
@@ -66,4 +66,16 @@ is('fooäàaáâåbar' ~~ m:m/<[a..b]>+/, 'äàaáâåba', 'Ignoremark with rang
 # Ensure that synthetics also properly can match the base character
 is "\c[LATIN SMALL LETTER J WITH CARON, COMBINING DOT BELOW]" ~~ /:m:i j /, 'ǰ̣', "Synthetics with decomposable base characters properly work with ignoremark";
 ok qq{"\c[ZERO WIDTH JOINER]a"} ~~ / (:ignoremark ^ '"' ) /, "Synthetics properly can be matched with ignoremark";
+is “{"\c[ARABIC NUMBER SIGN]" x 3}a” ~~ /:m a/, “{"\c[ARABIC NUMBER SIGN]" x 3}a”, "Igoremark supports Prepend";
+my Int:D $val = 0;
+for ^ 10 {
+    my Str:D $str =  "\c[arabic number sign]" x $_ ~ 'a';
+    $val++ if "\c[arabic number sign]" x $_ ~ 'a' ~~ /:m a/ eq $str;
+}
+ok $val == 10, "Ignoremark supports 0..9 prepend marks";
+is "\c[ARABIC NUMBER SIGN]" ~~ /:m "\c[ARABIC NUMBER SIGN]" /, "\c[ARABIC NUMBER SIGN]", "Ignoremark can match degenerate Prepend";
+is "\c[SYRIAC ABBREVIATION MARK, ARABIC NUMBER SIGN]" ~~ /:m "\c[SYRIAC ABBREVIATION MARK]" /, "\c[SYRIAC ABBREVIATION MARK, ARABIC NUMBER SIGN]", "Ignoremark matches the first codepoint for all Prepend degenerates";
+nok "\c[SYRIAC ABBREVIATION MARK, ARABIC NUMBER SIGN]" ~~ /:m "\c[ARABIC NUMBER SIGN]" /, "Ignoremark does not match the second codepoint for all Prepend degenerates";
+nok "\c[SYRIAC ABBREVIATION MARK, COMBINING CARON]" ~~ /:m "\c[COMBINING CARON]" /, "Ignoremark doesn't match second codepoint for Prepend+Extend degenerate";
+is "\c[SYRIAC ABBREVIATION MARK, COMBINING CARON]" ~~ /:m "\c[SYRIAC ABBREVIATION MARK]" /, "\c[SYRIAC ABBREVIATION MARK, COMBINING CARON]", "Ignoremark matches the first codepoint for all Prepend+Extend degenerates";
 # vim: syn=perl6 sw=4 ts=4 expandtab