precompilation tests for diamond releationship for RT #122773 hoelzro++.

Implemented using this hint from lizmat++ http://irclog.perlgeek.de/perl6/2014-09-23#i_9400516

S10-packages/precompilation.t

@@ -1,11 +1,41 @@
 use Test;
+use lib 't/spec/packages';
+use Test::Util;
 
-plan 1;
+plan 8;
+
+my @precomp-paths;
+
+%*ENV<PERL6LIB> = 't/spec/packages';
+
+for <C A B> {
+    my $path = "t/spec/packages/Example/{$_}.pm";
+    my $precomp-path = $path ~ '.' ~ $*VM.precomp-ext;
+    unlink $precomp-path if $precomp-path.IO.e;
+    ok CompUnit.new($path).precomp, "precomp Example::$_";
+    ok $precomp-path.IO.e, "created $precomp-path";
+    @precomp-paths.push: $precomp-path;
+}
+
+my @keys = Test::Util::run( q:to"--END--").lines;
+    use Example::A;
+    use Example::B;
+
+    .say for Example::.keys.sort;
+    --END--
+
+#?rakudo.jvm todo 'RT #122773'
+#?rakudo.moar todo 'RT #122773'
+is_deeply @keys, [<A B C>], 'Diamond Relationship';
+
+unlink $_ for @precomp-paths;
 
 # RT #76456
 {
     my $cur  = CompUnitRepo::Local::File.new("t/spec/packages");
+
     my ($cu) = $cur.candidates('RT76456');
     ok $cu.precomp(:force), 'precompiled a parameterized role';
     unlink $cu.precomp-path if $cu.precomp-path.IO.e;
 }
+