Add tests to verify that correct 'Content-Length' or 'Transfer-Encoding' headers are being set in PreparedRequest.

tests/test_requests.py

@@ -1693,6 +1693,30 @@ class TestRequests:
         resp.close()
         assert resp.raw.closed
 
+    def test_empty_stream_with_auth_does_not_set_content_length_header(self, httpbin):
+        """Ensure that a byte stream with size 0 will not set both a Content-Length
+        and Transfer-Encoding header
+        """
+        auth = ('user', 'pass')
+        url = httpbin('post')
+        file_obj = io.BytesIO(b'')
+        r = requests.Request('POST', url, auth=auth, data=file_obj)
+        prepared_request = r.prepare()
+        assert 'Transfer-Encoding' in prepared_request.headers
+        assert 'Content-Length' not in prepared_request.headers
+
+    def test_stream_with_auth_does_not_set_transfer_encoding_header(self, httpbin):
+        """Ensure that a byte stream with size > 0 will not set both a Content-Length
+        and Transfer-Encoding header"""
+        auth = ('user', 'pass')
+        url = httpbin('post')
+        file_obj = io.BytesIO(b'test data')
+        r = requests.Request('POST', url, auth=auth, data=file_obj)
+        prepared_request = r.prepare()
+        assert 'Transfer-Encoding' not in prepared_request.headers
+        assert 'Content-Length' in prepared_request.headers
+
+
 class TestCaseInsensitiveDict:
 
     @pytest.mark.parametrize(