fix(xml): refactor for lazy require

See #126

lua/neotest/lib/init.lua

@@ -9,7 +9,7 @@ M.xml = {
   ---@param xml_data string
   ---@return table
   parse = function(xml_data)
-    local handler = xml_tree:new()
+    local handler = xml_tree()
     local parser = xml.parser(handler)
     parser:parse(xml_data)
     return handler.root

lua/neotest/lib/xml/tree.lua

@@ -164,4 +164,6 @@ end
 ---Parses CDATA tag content.
 tree.cdata = tree.text
 tree.__index = tree
-return tree
+return function()
+  return tree:new()
+end

tests/unit/lib/xml_spec.lua

@@ -0,0 +1,43 @@
+local lib = require("neotest.lib")
+
+describe("When receiving valid XML", function()
+  it("it is parsed correctly", function()
+    local xml_data = [[<?xml version="1.0" encoding="UTF-8"?>
+<testsuites>
+  <testsuite name="TestProject\UserTest" file="my_file" tests="1" assertions="3" errors="0" warnings="0" failures="0" skipped="0" time="0.000923">
+    <testcase name="testClassConstructor" class="TestProject\UserTest" classname="TestProject.UserTest" file="my_file" line="13" assertions="3" time="0.000923"/>
+  </testsuite>
+</testsuites>]]
+
+    local expected = {
+      testsuites = {
+        testsuite = {
+          _attr = {
+            assertions = "3",
+            errors = "0",
+            failures = "0",
+            file = "my_file",
+            name = "TestProject\\UserTest",
+            skipped = "0",
+            tests = "1",
+            time = "0.000923",
+            warnings = "0",
+          },
+          testcase = {
+            _attr = {
+              assertions = "3",
+              class = "TestProject\\UserTest",
+              classname = "TestProject.UserTest",
+              file = "my_file",
+              line = "13",
+              name = "testClassConstructor",
+              time = "0.000923",
+            },
+          },
+        },
+      },
+    }
+
+    assert.are.same(lib.xml.parse(xml_data), expected)
+  end)
+end)