test: mark the jruby tests from sparklemotion#2379 as pending

See context in sparklemotion#2380. The fix on JRuby is expensive and is probably
not worth the investment of developer time right now.

But let's preserve those failures as a known issue by introducing the
`pending` and `pending_if` test helpers.

test/helper.rb

@@ -196,6 +196,20 @@ def assert_not_send(send_ary, m = nil)
       refute(recv.__send__(msg, *args), m)
     end unless method_defined?(:assert_not_send)
 
+    def pending(msg)
+      begin
+        yield
+      rescue MiniTest::Assertion
+        skip("pending #{msg}")
+      end
+      flunk("pending test unexpectedly passed: #{msg}")
+    end
+
+    def pending_if(msg, pend_eh, &block)
+      return yield unless pend_eh
+      pending(msg, &block)
+    end
+
     def i_am_ruby_matching(gem_version_requirement_string)
       Gem::Requirement.new(gem_version_requirement_string).satisfied_by?(Gem::Version.new(RUBY_VERSION))
     end

test/xml/test_node.rb

@@ -1273,7 +1273,9 @@ def test_wrap
             eoxml
 
             set = xml.search("//b")
-            assert_equal(3, set[0].line)
+            pending_if("https://github.com/sparklemotion/nokogiri/issues/2380", Nokogiri.jruby?) do
+              assert_equal(3, set[0].line)
+            end
           end
 
           it "properly numbers lines with documents containing XML comments" do
@@ -1307,7 +1309,9 @@ def test_wrap
             eoxml
 
             set = xml.search("//c")
-            assert_equal(6, set[0].line)
+            pending_if("https://github.com/sparklemotion/nokogiri/issues/2380", Nokogiri.jruby?) do
+              assert_equal(6, set[0].line)
+            end
           end
 
           it "returns a sensible line number for each node" do