Previously, MockHttpServletRequest allowed its body to be ready
multiple times using its InputStream. As of recent Spring Framework
5.1 snapshots, this is no longer the case.
This commit moves to directly accessing the request's content as a
byte array using getContentAsByteArray() which was introduced in
Framework 5.0.
Closes gh-515
Previously, the query string was only parsed when converted a GET
request. This commit updates WebTestClientRequestConverter to
parse the query string for all requests irrespective of the method.
Closes gh-472
