TestApp._get_request does not use the Request's charset about webtest HOT 2 CLOSED

diff --git a/webtest/app.py b/webtest/app.py
index 32a0ef9..524972d 100644
--- a/webtest/app.py
+++ b/webtest/app.py
@@ -799,11 +799,13 @@ class TestApp(object):
             environ['QUERY_STRING'] = ''
         if content_type is not None:
             environ['CONTENT_TYPE'] = content_type
-        environ['CONTENT_LENGTH'] = str(len(params))
         environ['REQUEST_METHOD'] = method
-        environ['wsgi.input'] = BytesIO(to_bytes(params))
         url = self._remove_fragment(url)
         req = self.RequestClass.blank(url, environ)
+        if isinstance(params, text_type):
+            req.text = params
+        else:
+            req.body = params
         if headers:
             req.headers.update(headers)
         return self.do_request(req, status=status,