pythonGH-105973 Update test to test multiple header whitespace permut…

…ations

Although python#105973 is promarily concerned with trailing whitespace not
being stripped, it's easy/inexpensive to test for other whitespace
behaviour (to detect any other future incompatabilities).

This test change ensures that

- Leading whitespace is trimmed from header values
- Whitespace in the middle of a header value is not removed

Lib/test/test_httplib.py

@@ -369,13 +369,20 @@ def test_headers_debuglevel(self):
         self.assertEqual(lines[3], "header: Second: val2")
 
     def test_header_whitespace_removal(self):
-        request = b"Host: example.com\r\nContent-Length: 12 \r\n\r\n"
+        request = b"Host: example.com\r\nContent-Length: 12 \r\nuser-agent: web browser \r\n"
         fh = io.BytesIO(request)
         parsed = client.parse_headers(fh)
 
         # Check whether the trailing whitespace has been preserved
         self.assertTrue(parsed.get('content-length') == "12",
-                        'Header parsing did not strip trailing whitespace from value')
+                        'Header parsing did not strip trailing whitespace from header value')
+        # And whether leading has been preserved
+        self.assertTrue(parsed.get('host') == "example.com",
+                        'Header parsing did not strip leading whitespace from header value')
+        # whitespace within header values should be preserved
+        self.assertTrue(parsed.get('user-agent') == "web browser",
+                        'Header parsing stripped whitespace from middle of header value')
+
 
 class HttpMethodTests(TestCase):
     def test_invalid_method_names(self):