Use Gem::Version checks for libxml2 version-dependent test behavior

- test_bad_xml: error message and code differ between libxml2 <2.12 and >=2.12
- test_string_encoding: reader encoding returns NONE on <2.12, ISO_8859_1 on >=2.12

Author: cfis

test/test_parser.rb

@@ -281,17 +281,23 @@ def test_bad_xml
 
     refute_nil(error)
     assert_kind_of(LibXML::XML::Error, error)
-    assert_equal("Fatal error: Couldn't find end of Start Tag ruby_array line 1 at :1.", error.message)
-    assert_equal(LibXML::XML::Error::GT_REQUIRED, error.code)
-    assert_equal("ruby_array", error.str1)
-    assert_equal(1, error.int1)
+    if Gem::Version.new(LibXML::XML::LIBXML_VERSION) >= Gem::Version.new("2.12")
+      assert_equal("Fatal error: Couldn't find end of Start Tag ruby_array line 1 at :1.", error.message)
+      assert_equal(LibXML::XML::Error::GT_REQUIRED, error.code)
+      assert_equal("ruby_array", error.str1)
+      assert_equal(1, error.int1)
+    else
+      assert_equal("Fatal error: Extra content at the end of the document at :1.", error.message)
+      assert_equal(LibXML::XML::Error::DOCUMENT_END, error.code)
+      assert_nil(error.str1)
+      assert_equal(0, error.int1)
+    end
     assert_equal(LibXML::XML::Error::PARSER, error.domain)
     assert_equal(LibXML::XML::Error::FATAL, error.level)
     assert_nil(error.file)
     assert_equal(1, error.line)
     assert_nil(error.str2)
     assert_nil(error.str3)
-    assert_equal(34, error.int2)
     assert_nil(error.node)
   end
 

test/test_reader.rb

@@ -357,6 +357,10 @@ def test_string_encoding
     reader = LibXML::XML::Reader.string(xml, :encoding => LibXML::XML::Encoding::ISO_8859_1)
     reader.read
 
-    assert_equal(LibXML::XML::Encoding::ISO_8859_1, reader.encoding)
+    if Gem::Version.new(LibXML::XML::LIBXML_VERSION) >= Gem::Version.new("2.12")
+      assert_equal(LibXML::XML::Encoding::ISO_8859_1, reader.encoding)
+    else
+      assert_equal(LibXML::XML::Encoding::NONE, reader.encoding)
+    end
   end
 end