Use !empty? instead of length > 0.

Addressing rubocop warning.

Author: isimluk

test/ds/arf_test.rb

@@ -60,7 +60,7 @@ def test_create_arf_and_get_profile
   def test_new_memory
     create_arf
     raw_data = File.read(REPORT)
-    assert raw_data.length > 0
+    refute raw_data.empty?
     arf = OpenSCAP::DS::Arf.new :content => raw_data, :path => REPORT
     arf.destroy
   end

test/source_test.rb

@@ -32,7 +32,7 @@ def test_source_new_ok
 
   def test_source_new_memory
     raw_data = File.read('../data/xccdf.xml')
-    assert raw_data.length > 0
+    refute raw_data.empty?
     s = OpenSCAP::Source.new(:content => raw_data, :path => '/mytestpath')
     s.destroy
   end