Add t/run/todo.t

This is a place for tests for unfixed bugs.

Such bugs may resurface later in the same or somewhat different form,
and we could easily overlook the fact that they are duplicates.  By
adding TODO tests here, we would automatically get notified that an
earlier ticket is fixed when such a later one gets fixed.

It is my guess that some open tickets are already fixed and we just
don't know it.

And it would save time for the proect to not have to go to the issues
list and refigure out how to reproduce them, as we periodically do.

It would be a good getting-started task for people new to the project to
go through our bug list and copy the example failing code snippets into
this file.

Author: khwilliamson

MANIFEST

@@ -6628,6 +6628,7 @@ t/run/switchx.aux			Data for switchx.t
 t/run/switchx.t				Test the -x switch
 t/run/switchx2.aux			Data for switchx.t
 t/run/switchx3.aux			Data for switchx.t
+t/run/todo.t				TODO tests
 t/TEST					The regression tester
 t/test.pl				Simple testing library
 t/test_pl/_num_to_alpha.t		Tests for the simple testing library

t/run/todo.t

@@ -0,0 +1,39 @@
+#!./perl
+BEGIN {
+    chdir 't' if -d 't';
+    @INC = '../lib';
+    require './test.pl';    # for fresh_perl_is() etc
+}
+
+use strict;
+use warnings;
+
+# This file is a place for tests that fail at the time they are added here.
+#
+# When a ticket is filed, just follow the paradigm(s) in this file to add a
+# test that shows the failure.
+#
+# It is expected that when new tickets are opened, some will actually be
+# duplicates of existing known bad behavior.  And since there are so many open
+# tickets, we might overlook that.  If there is a test here, we would
+# automatically discover that a fix for the newer ticket actually fixed an
+# earlier one (or ones) as well.  Thus the issue can be closed, and the final
+# disposition of the test here determined at that time.  (For example, perhaps
+# it is redundant to the test demonstrating the bug that was intentionally
+# fixed, so can be removed altogether.)
+
+my $switches = "";
+
+our $TODO;
+TODO: {
+    local $TODO = "GH 16250";
+    fresh_perl_is(<<~'EOF',
+        "abcde5678" =~ / b (*pla:.*(*plb:(*plb:(.{4}))? (.{5})).$)/x;
+        print $1 // "undef", ":", $2 // "undef", "\n";
+        "abcde5678" =~ / b .* (*plb:(*plb:(.{4}))? (.{5}) ) .$ /x;
+        print $1 // "undef", ":", $2 // "undef", "\n";
+        EOF
+    "undef:de567\nundef:de567", { $switches }, "");
+}
+
+done_testing();