If Readonly::XS is installed, t/json.t (introduced in boolean.pm 0.29) fails.

gistfile1.txt

% cd boolean-0.30
% make test
PERL_DL_NONLAZY=1 /opt/perl/perlbrew/perls/perl-5.16/bin/perl "-MExtUtils::Command::MM" "-e" "test_harness(0, 'inc', 'blib/lib', 'blib/arch')" t/*.t
t/boolean.t .. ok
t/export.t ... ok
t/json.t ..... # No tests run!
t/json.t ..... Dubious, test returned 255 (wstat 65280, 0xff00)
Failed 2/2 subtests
t/truth.t .... ok

Test Summary Report
-------------------
t/json.t   (Wstat: 65280 Tests: 0 Failed: 0)
  Non-zero exit status: 255
  Parse errors: Bad plan.  You planned 2 tests but ran 0.
Files=4, Tests=97,  0 wallclock secs ( 0.03 usr  0.01 sys +  0.08 cusr  0.00 csys =  0.12 CPU)
Result: FAIL
Failed 1/4 test programs. 0/97 subtests failed.
make: *** [test_dynamic] Error 255

% perl -Ilib t/json.t
1..2
# No tests run!

(with both Readonly::XS and JSON::XS)
% perl -Mboolean=-truth -MJSON -e 'my $json=JSON->new->convert_blessed; print $json->encode({false => (0 == 1)})'
Modification of a read-only value attempted at -e line 1.

------ Append 4/10
(without JSON::XS but with Readonly::XS)
% pm-uninstall JSON::XS
% perl -Mboolean=-truth -MJSON -e 'my $json=JSON->new->convert_blessed; print $json->encode({false => (0 == 1)})'
{"1":false}

(without Readonly::XS but with JSON::XS)
% cpanm JSON::XS
% pm-uninstall Readonly::XS
% perl -Mboolean=-truth -MJSON -e 'my $json=JSON->new->convert_blessed; print $json->encode({1 => (0 == 1)})'
{"1":false}