Only use coveralls and simplecov on RUBY_ENGINE=ruby

.travis.yml

@@ -8,4 +8,4 @@ rvm:
   - jruby-9.2.8.0
   - truffleruby
 script:
-  - bundle exec rake test_with_coveralls
+  - bundle exec rake ci

Gemfile

@@ -6,5 +6,8 @@ gem 'rake', '~> 13'
 gem 'minitest', '~> 5'
 gem 'webmock', '~> 3'
 gem 'yard', '~> 0.9'
-gem 'simplecov', '~> 0.16'
-gem 'coveralls', '~> 0.8'
+
+platforms :ruby do
+  gem 'simplecov', '~> 0.16'
+  gem 'coveralls', '~> 0.8'
+end

Rakefile

@@ -1,6 +1,5 @@
 require 'rake/testtask'
 require 'yard'
-require 'coveralls/rake/task'
 
 task :default => :test
 
@@ -11,6 +10,12 @@ end
 
 YARD::Rake::YardocTask.new
 
-Coveralls::RakeTask.new
+if defined?(RUBY_ENGINE) && RUBY_ENGINE == 'ruby'
+  require 'coveralls/rake/task'
 
-task :test_with_coveralls => [:test, 'coveralls:push']
+  Coveralls::RakeTask.new
+
+  task :ci => [:test, 'coveralls:push']
+else
+  task :ci => :test
+end

test/nexmo/test.rb

@@ -1,7 +1,9 @@
-require 'simplecov'
+if defined?(RUBY_ENGINE) && RUBY_ENGINE == 'ruby'
+  require 'simplecov'
 
-SimpleCov.start do
-  add_filter 'test/nexmo'
+  SimpleCov.start do
+    add_filter 'test/nexmo'
+  end
 end
 
 require 'minitest/autorun'