Improved tests [skip ci]

Author: ankane

test/booster_test.rb

@@ -64,6 +64,8 @@ def test_predict_daru
   end
 
   def test_predict_rover
+    skip if jruby?
+
     require "rover"
     x_test =
       Rover::DataFrame.new([

test/dataset_test.rb

@@ -65,7 +65,7 @@ def test_daru
   end
 
   def test_numo
-    skip if RUBY_PLATFORM == "java"
+    skip if jruby?
 
     require "numo/narray"
     data = Numo::DFloat.new(3, 5).seq
@@ -75,7 +75,7 @@ def test_numo
   end
 
   def test_rover
-    skip if RUBY_PLATFORM == "java"
+    skip if jruby?
 
     require "rover"
     data = Rover.read_csv(data_path)

test/test_helper.rb

@@ -103,4 +103,8 @@ def teardown
   def tempfile
     @tempfile ||= "#{Dir.mktmpdir}/#{Time.now.to_f}"
   end
+
+  def jruby?
+    RUBY_PLATFORM == "java"
+  end
 end