[ruby/uri] Added test for constant definition and remove URI::REGEXP when using RFC3986_PARSER

https://github.com/ruby/uri/commit/6f616d97fc

lib/uri/common.rb

@@ -26,8 +26,8 @@ module URI
     remove_const(:Parser) if defined?(Parser)
     const_set("Parser", parser.class)
 
+    remove_const(:REGEXP) if defined?(REGEXP)
     if Parser == RFC2396_Parser
-      remove_const(:REGEXP) if defined?(REGEXP)
       const_set("REGEXP", URI::RFC2396_REGEXP)
       Parser.new.pattern.each_pair do |sym, str|
         unless REGEXP::PATTERN.const_defined?(sym)
@@ -35,6 +35,7 @@ module URI
         end
       end
     end
+
     Parser.new.regexp.each_pair do |sym, str|
       remove_const(sym) if const_defined?(sym)
       const_set(sym, str)

test/uri/test_common.rb

@@ -10,6 +10,23 @@ class URI::TestCommon < Test::Unit::TestCase
   def teardown
   end
 
+  def test_parser_switch
+    assert_equal(URI::Parser, URI::RFC3986_Parser)
+    refute defined?(::URI::REGEXP)
+
+    URI.parser = URI::RFC2396_PARSER
+
+    assert_equal(URI::Parser, URI::RFC2396_Parser)
+    assert defined?(URI::REGEXP)
+
+    URI.parser = URI::RFC3986_PARSER
+
+    assert_equal(URI::Parser, URI::RFC3986_Parser)
+    refute defined?(URI::REGEXP)
+  ensure
+    URI.parser = URI::RFC3986_PARSER
+  end
+
   def test_extract
     EnvUtil.suppress_warning do
       assert_equal(['http://example.com'],