update test for url_for and update routing.md doc

docs/sanic/routing.md

@@ -145,6 +145,28 @@ Other things to keep in mind when using `url_for`:
 url = app.url_for('post_handler', post_id=5, arg_one='one', arg_two='two')
 # /posts/5?arg_one=one&arg_two=two
 ```
+- Multivalue argument can be passed to `url_for`. For example:
+```python
+url = app.url_for('post_handler', post_id=5, arg_one=['one', 'two'])
+# /posts/5?arg_one=one&arg_one=two
+```
+- Also some special arguments (`_anchor`, `_external`, `_scheme`, `_method`, `_server`) passed to `url_for` will have special url building (`_method` is not support now and will be ignored). For example:
+```python
+url = app.url_for('post_handler', post_id=5, arg_one='one', _anchor='anchor')
+# /posts/5?arg_one=one#anchor
+
+url = app.url_for('post_handler', post_id=5, arg_one='one', _external=True)
+# //server/posts/5?arg_one=one
+# _external requires passed argument _server or SERVER_NAME in app.config or url will be same as no _external
+
+url = app.url_for('post_handler', post_id=5, arg_one='one', _scheme='http', _external=True)
+# http://server/posts/5?arg_one=one
+# when specifying _scheme, _external must be True
+
+# you can pass all special arguments one time
+url = app.url_for('post_handler', post_id=5, arg_one=['one', 'two'], arg_two=2, _anchor='anchor', _scheme='http', _external=True, _server='another_server:8888')
+# http://another_server:8888/posts/5?arg_one=one&arg_one=two&arg_two=2#anchor
+```
 - All valid parameters must be passed to `url_for` to build a URL. If a parameter is not supplied, or if a parameter does not match the specified type, a `URLBuildError` will be thrown.
 
 

sanic/sanic.py

@@ -283,8 +283,7 @@ class Sanic:
                 replacement_regex, supplied_param, out)
 
         # parse the remainder of the keyword arguments into a querystring
-        if kwargs:
-            query_string = urlencode(kwargs, doseq=True)
+        query_string = urlencode(kwargs, doseq=True) if kwargs else ''
         # scheme://netloc/path;parameters?query#fragment
         out = urlunparse((scheme, netloc, out, '', query_string, anchor))
 

tests/test_url_building.py

@@ -10,6 +10,14 @@ from sanic.exceptions import URLBuildError
 
 import string
 
+URL_FOR_ARGS1 = dict(arg1=['v1', 'v2'])
+URL_FOR_VALUE1 = '/myurl?arg1=v1&arg1=v2'
+URL_FOR_ARGS2 = dict(arg1=['v1', 'v2'], _anchor='anchor')
+URL_FOR_VALUE2 = '/myurl?arg1=v1&arg1=v2#anchor'
+URL_FOR_ARGS3 = dict(arg1='v1', _anchor='anchor', _scheme='http',
+                     _server='localhost:{}'.format(test_port), _external=True)
+URL_FOR_VALUE3 = 'http://localhost:{}/myurl?arg1=v1#anchor'.format(test_port)
+
 
 def _generate_handlers_from_names(app, l):
     for name in l:
@@ -39,28 +47,21 @@ def test_simple_url_for_getting(simple_app):
         assert response.text == letter
 
 
-def test_simple_url_for_getting_with_duplicate_params(simple_app):
-    kw = dict(arg1=['value1', 'value2'], _anchor='anchor')
-    for letter in string.ascii_letters:
-        url = simple_app.url_for(letter, **kw)
+@pytest.mark.parametrize('args,url',
+                         [(URL_FOR_ARGS1, URL_FOR_VALUE1),
+                          (URL_FOR_ARGS2, URL_FOR_VALUE2),
+                          (URL_FOR_ARGS3, URL_FOR_VALUE3)])
+def test_simple_url_for_getting_with_more_params(args, url):
+    app = Sanic('more_url_build')
 
-        assert url == '/{}?arg1=value1&arg1=value2#anchor'.format(letter)
-        request, response = sanic_endpoint_test(simple_app, uri=url)
+    @app.route('/myurl')
+    def passes(request):
+        return text('this should pass')
+
+    assert url == app.url_for('passes', **args)
+    request, response = sanic_endpoint_test(app, uri=url)
     assert response.status == 200
-        assert response.text == letter
-
-
-def test_simple_url_for_getting_with_special_params(simple_app):
-    kw = dict(arg1='value1', _anchor='anchor', _scheme='http',
-              _server='localhost:{}'.format(test_port), _external=True)
-    url_fmt = 'http://localhost:{}/{}?arg1=value1#anchor'
-    for letter in string.ascii_letters:
-        url = simple_app.url_for(letter, **kw)
-
-        assert url == url_fmt.format(test_port, letter)
-        request, response = sanic_endpoint_test(simple_app, uri=url)
-        assert response.status == 200
-        assert response.text == letter
+    assert response.text == 'this should pass'
 
 
 def test_fails_if_endpoint_not_found():