xml2: Add tests for functions xpath_nodeset() and xpath_list()

These two functions with their different argument lists have never been
tested in this module, so let's add something.

Author: Ronan Dunklau
Discussion: https://postgr.es/m/ZzMSJkiNZhimjXWx@paquier.xyz

contrib/xml2/expected/xml2.out

@@ -207,6 +207,45 @@ SELECT xslt_process('<employee><name>cim</name><age>30</age><pay>400</pay></empl
  
 (1 row)
 
+-- xpath_nodeset()
+SELECT xpath_nodeset(article_xml::text, '/article/author|/article/pages')
+  FROM articles;
+             xpath_nodeset              
+----------------------------------------
+ <author>test</author><pages>37</pages>
+(1 row)
+
+SELECT xpath_nodeset(article_xml::text, '/article/author|/article/pages',
+                     'item_without_toptag')
+  FROM articles;
+                                                        xpath_nodeset                                                         
+------------------------------------------------------------------------------------------------------------------------------
+ <item_without_toptag><author>test</author></item_without_toptag><item_without_toptag><pages>37</pages></item_without_toptag>
+(1 row)
+
+SELECT xpath_nodeset(article_xml::text, '/article/author|/article/pages',
+                     'result', 'item')
+  FROM articles;
+                                   xpath_nodeset                                   
+-----------------------------------------------------------------------------------
+ <result><item><author>test</author></item><item><pages>37</pages></item></result>
+(1 row)
+
+-- xpath_list()
+SELECT xpath_list(article_xml::text, '/article/author|/article/pages')
+  FROM articles;
+ xpath_list 
+------------
+ test,37
+(1 row)
+
+SELECT xpath_list(article_xml::text, '/article/author|/article/pages', '|')
+  FROM articles;
+ xpath_list 
+------------
+ test|37
+(1 row)
+
 -- possible security exploit
 SELECT xslt_process('<xml><foo>Hello from XML</foo></xml>',
 $$<xsl:stylesheet version="1.0"

contrib/xml2/expected/xml2_1.out

@@ -151,6 +151,45 @@ SELECT xslt_process('<employee><name>cim</name><age>30</age><pay>400</pay></empl
   </xsl:template>
 </xsl:stylesheet>$$::text, 'n1="v1",n2="v2",n3="v3",n4="v4",n5="v5",n6="v6",n7="v7",n8="v8",n9="v9",n10="v10",n11="v11",n12="v12"'::text);
 ERROR:  xslt_process() is not available without libxslt
+-- xpath_nodeset()
+SELECT xpath_nodeset(article_xml::text, '/article/author|/article/pages')
+  FROM articles;
+             xpath_nodeset              
+----------------------------------------
+ <author>test</author><pages>37</pages>
+(1 row)
+
+SELECT xpath_nodeset(article_xml::text, '/article/author|/article/pages',
+                     'item_without_toptag')
+  FROM articles;
+                                                        xpath_nodeset                                                         
+------------------------------------------------------------------------------------------------------------------------------
+ <item_without_toptag><author>test</author></item_without_toptag><item_without_toptag><pages>37</pages></item_without_toptag>
+(1 row)
+
+SELECT xpath_nodeset(article_xml::text, '/article/author|/article/pages',
+                     'result', 'item')
+  FROM articles;
+                                   xpath_nodeset                                   
+-----------------------------------------------------------------------------------
+ <result><item><author>test</author></item><item><pages>37</pages></item></result>
+(1 row)
+
+-- xpath_list()
+SELECT xpath_list(article_xml::text, '/article/author|/article/pages')
+  FROM articles;
+ xpath_list 
+------------
+ test,37
+(1 row)
+
+SELECT xpath_list(article_xml::text, '/article/author|/article/pages', '|')
+  FROM articles;
+ xpath_list 
+------------
+ test|37
+(1 row)
+
 -- possible security exploit
 SELECT xslt_process('<xml><foo>Hello from XML</foo></xml>',
 $$<xsl:stylesheet version="1.0"

contrib/xml2/sql/xml2.sql

@@ -123,6 +123,22 @@ SELECT xslt_process('<employee><name>cim</name><age>30</age><pay>400</pay></empl
   </xsl:template>
 </xsl:stylesheet>$$::text, 'n1="v1",n2="v2",n3="v3",n4="v4",n5="v5",n6="v6",n7="v7",n8="v8",n9="v9",n10="v10",n11="v11",n12="v12"'::text);
 
+-- xpath_nodeset()
+SELECT xpath_nodeset(article_xml::text, '/article/author|/article/pages')
+  FROM articles;
+SELECT xpath_nodeset(article_xml::text, '/article/author|/article/pages',
+                     'item_without_toptag')
+  FROM articles;
+SELECT xpath_nodeset(article_xml::text, '/article/author|/article/pages',
+                     'result', 'item')
+  FROM articles;
+
+-- xpath_list()
+SELECT xpath_list(article_xml::text, '/article/author|/article/pages')
+  FROM articles;
+SELECT xpath_list(article_xml::text, '/article/author|/article/pages', '|')
+  FROM articles;
+
 -- possible security exploit
 SELECT xslt_process('<xml><foo>Hello from XML</foo></xml>',
 $$<xsl:stylesheet version="1.0"