Revert "Remove newly added test for open with :ra mode"

This reverts commit 418466f.

cmp. https://irclog.perlgeek.de/perl6-dev/2017-04-13#i_14424307

Author: usev6

S32-io/open.t

@@ -251,6 +251,27 @@ LEAVE unlink PATH;
     $fh.close;
 }
 
+# test :ra mode
+#?rakudo.jvm skip '[io grant] IllegalArgumentException: READ + APPEND not allowed'
+{   unlink PATH;
+    my $fh;
+
+    $fh = open PATH, :ra;
+    ok defined($fh), 'can open non-existent file in :ra mode';
+    $fh.print('onions are tasty');
+    $fh.close;
+
+    $fh = open PATH, :ra;
+    ok defined($fh), 'can open existing file in :ra mode';
+    $fh.print('cats say meow');
+
+    $fh.seek(0, SeekFromBeginning);
+    is $fh.lines.join, 'onions are tastycats say meow',
+        'can read in :append mode and it appends to existing data';
+
+    $fh.close;
+}
+
 # test :create mode
 #?rakudo.jvm skip "[io grant] NoSuchFileException: t-32-io-open.tmp'"
 {   unlink PATH;