Logstash:Event tests failing with : "expect(subject.sprintf("%{message}").encoding).to eq(Encoding::UTF_8)"

Logstash Version: 5.0.0.dev (master)
Platform : IBM Power PC

I could run the binary on the platform with no issues; however the unit-tests for core are failing; the command being used "rake test:core". All the 4 failures which I am getting are similar, please find the partial log of errors as below:

```
1) LogStash::Event using hash input from deserialized json behaves like all event tests #sprintf #encoding should return unknown patterns as UTF-8
Failure/Error: expect(subject.sprintf("%{unkown_pattern}").encoding).to eq(Encoding::UTF_8)

expected: #
got: #

(compared using ==)

Diff:
@@ -1,2 +1,2 @@
-#
+#
Shared Example Group: "all event tests" called from ./logstash-core-event/spec/logstash/event_spec.rb:582
# ./logstash-core-event/spec/logstash/event_spec.rb:194:in `(root)'
# ./vendor/bundle/jruby/1.9/gems/rspec-wait-0.0.8/lib/rspec/wait.rb:46:in `(root)'
# ./lib/bootstrap/rspec.rb:11:in `(root)'
```

The jruby version I have installed is jruby 1.7.25.
Has anyone experienced similar issue before? Any pointers would be helpful.
Thanks in advance.