Add a unit test that checks we didn't break booleans with the new COW…

… static const behaviour

MANIFEST

@@ -5830,6 +5830,7 @@ t/op/auto.t			See if autoincrement et all work
 t/op/avhv.t			See if pseudo-hashes work
 t/op/bless.t			See if bless works
 t/op/blocks.t			See if BEGIN and friends work
+t/op/bool.t			Check misc details of boolean values
 t/op/bop.t			See if bitops work
 t/op/caller.pl			Tests shared between caller.t and XS op.t
 t/op/caller.t			See if caller() works

t/op/bool.t

@@ -0,0 +1,37 @@
+#!./perl
+
+BEGIN {
+    chdir 't' if -d 't';
+    require './test.pl';
+    set_up_inc('../lib');
+}
+
+use strict;
+use warnings;
+
+my $truevar  = (5 == 5);
+my $falsevar = (5 == 6);
+
+cmp_ok($truevar, '==', 1);
+cmp_ok($truevar, 'eq', "1");
+
+cmp_ok($falsevar, '==', 0);
+cmp_ok($falsevar, 'eq', "");
+
+{
+    # Check that boolean COW string buffer is safe to copy into new SVs and
+    # doesn't get corrupted by inplace mutations
+    my $x = $truevar;
+    $x =~ s/1/t/;
+
+    cmp_ok($x, 'eq', "t");
+    cmp_ok($truevar, 'eq', "1");
+
+    my $y = $truevar;
+    substr($y, 0, 1, "T");
+
+    cmp_ok($y, 'eq', "T");
+    cmp_ok($truevar, 'eq', "1");
+}
+
+done_testing();