diff --git a/collects/tests/mzscheme/net.ss b/collects/tests/mzscheme/net.ss
index 011d88ae2a..bd52742325 100644
--- a/collects/tests/mzscheme/net.ss
+++ b/collects/tests/mzscheme/net.ss
@@ -3,68 +3,112 @@
 
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;;
-;; url parsing tests
+;; url.ss tests
 ;;
 
 (require (lib "url.ss" "net"))
 
 (let ()
   (define (test-s->u vec str)
-    (define (string->url/vec str)
-      (let ([res (string->url str)])
-        (vector (url-scheme res)
-                (url-user res)
-                (url-host res)
-                (url-port res)
-                (map (lambda (x) (if (string? x)
-                                     x
-                                     (vector (path/param-path x) (path/param-param x))))
-                     (url-path res))
-                (url-query res)
-                (url-fragment res))))
-    (define (url/vec->string vec)
-      (url->string
-       (make-url
-        (vector-ref vec 0)
-        (vector-ref vec 1)
-        (vector-ref vec 2)
-        (vector-ref vec 3)
-        (map (lambda (x) (if (string? x)
-                             x
-                             (make-path/param (vector-ref x 0) (vector-ref x 1))))
-             (vector-ref vec 4))
-        (vector-ref vec 5)
-        (vector-ref vec 6))))
-    
+    (define (string->url/vec str) (url->vec (string->url str)))
+    (define (url/vec->string vec) (url->string (vec->url vec)))
     (test vec string->url/vec str)
     (test str url/vec->string vec))
   
-  (test-s->u (vector "http" #f "www.google.com" #f '() #f #f)
-             "http://www.google.com/")
-  (test-s->u (vector "http" #f "www.google.com" #f (list "a" "b" "c") #f #f)
-             "http://www.google.com/a/b/c")
-  (test-s->u (vector "http" "robby" "www.google.com" #f (list "a" "b" "c") #f #f)
-             "http://robby@www.google.com/a/b/c")
-  (test-s->u (vector "http" #f "www.google.com" 8080 (list "a" "b" "c") #f #f)
-             "http://www.google.com:8080/a/b/c")
-  (test-s->u (vector "http" #f "www.google.com" #f (list "a" "b" "c") #f "joe")
-             "http://www.google.com/a/b/c#joe")
-  (test-s->u (vector "http" #f "www.google.com" #f (list "a" "b" "c") "tim" #f)
-             "http://www.google.com/a/b/c?tim")
-  (test-s->u (vector "http" #f "www.google.com" #f (list "a" "b" "c") "tim" "joe")
-             "http://www.google.com/a/b/c?tim#joe")
-  (test-s->u (vector "http" #f "www.google.com" #f (list "a" "b" #("c" "b")) #f #f)
-             "http://www.google.com/a/b/c;b")
-  (test-s->u (vector "http" #f "www.google.com" #f (list #("a" "x") "b" #("c" "b")) #f #f)
-             "http://www.google.com/a;x/b/c;b")
+  (define (test-c-u/r expected base relative)
+    (define (combine-url/relative-vec x y)
+      (url->vec (combine-url/relative (vec->url x) y)))
+    (test (url->vec expected) combine-url/relative-vec (url->vec base) relative))
+  
+  (define (vec->url vec)
+    (make-url
+     (vector-ref vec 0)
+     (vector-ref vec 1)
+     (vector-ref vec 2)
+     (vector-ref vec 3)
+     (map (lambda (x) (if (string? x)
+                          x
+                          (make-path/param (vector-ref x 0) (vector-ref x 1))))
+          (vector-ref vec 4))
+     (vector-ref vec 5)
+     (vector-ref vec 6)))
+  
+  (define (url->vec url)
+    (vector (url-scheme url)
+            (url-user url)
+            (url-host url)
+            (url-port url)
+            (map (lambda (x) (if (string? x)
+                                 x
+                                 (vector (path/param-path x) (path/param-param x))))
+                 (url-path url))
+            (url-query url)
+            (url-fragment url)))
+  
+  (test-s->u (vector #f #f #f #f '("") #f #f)
+             "/")
+  (test-s->u (vector #f #f #f #f '() #f #f)
+             "")
+  (test-s->u (vector "http" #f "www.drscheme.org" #f '("") #f #f)
+             "http://www.drscheme.org/")
+  (test-s->u (vector "http" #f "www.drscheme.org" #f (list "a" "b" "c") #f #f)
+             "http://www.drscheme.org/a/b/c")
+  (test-s->u (vector "http" "robby" "www.drscheme.org" #f (list "a" "b" "c") #f #f)
+             "http://robby@www.drscheme.org/a/b/c")
+  (test-s->u (vector "http" #f "www.drscheme.org" 8080 (list "a" "b" "c") #f #f)
+             "http://www.drscheme.org:8080/a/b/c")
+  (test-s->u (vector "http" #f "www.drscheme.org" #f (list "a" "b" "c") #f "joe")
+             "http://www.drscheme.org/a/b/c#joe")
+  (test-s->u (vector "http" #f "www.drscheme.org" #f (list "a" "b" "c") "tim" #f)
+             "http://www.drscheme.org/a/b/c?tim")
+  (test-s->u (vector "http" #f "www.drscheme.org" #f (list "a" "b" "c") "tim" "joe")
+             "http://www.drscheme.org/a/b/c?tim#joe")
+  (test-s->u (vector "http" #f "www.drscheme.org" #f (list "a" "b" #("c" "b")) #f #f)
+             "http://www.drscheme.org/a/b/c;b")
+  (test-s->u (vector "http" #f "www.drscheme.org" #f (list #("a" "x") "b" #("c" "b")) #f #f)
+             "http://www.drscheme.org/a;x/b/c;b")
   
   ;; test unquoting for %
-  (test-s->u (vector "http" #f "www.google.com" #f (list "a" "b" "c") "ti#m" "jo e")
-             "http://www.google.com/a/b/c?ti%23m#jo%20e")
-  (test-s->u (vector "http" #f "www.google.com" #f (list #("a " " a") " b " " c ") #f #f)
-             "http://www.google.com/a ; a/ b / c ")
-  (test-s->u (vector "http" "robb y" "www.google.com" #f '() #f #f)
-             "http://robb%20y@www.google.com/"))
+  (test-s->u (vector "http" #f "www.drscheme.org" #f (list "a" "b" "c") "ti#m" "jo e")
+             "http://www.drscheme.org/a/b/c?ti%23m#jo%20e")
+  (test-s->u (vector "http" #f "www.drscheme.org" #f (list #("a " " a") " b " " c ") #f #f)
+             "http://www.drscheme.org/a ; a/ b / c ")
+  (test-s->u (vector "http" "robb y" "www.drscheme.org" #f '("") #f #f)
+             "http://robb%20y@www.drscheme.org/")
+  
+  (let ([empty-url (make-url #f #f #f #f '() #f #f)])
+    (test-c-u/r (string->url "http://www.drscheme.org")
+                empty-url
+                "http://www.drscheme.org")
+    (test-c-u/r (string->url "http://www.drscheme.org")
+                (string->url "http://www.drscheme.org")
+                ""))
+  
+  (test-c-u/r (string->url "http://www.mzscheme.org")
+              (string->url "http://www.drscheme.org/")
+              "http://www.mzscheme.org")
+  (test-c-u/r (string->url "http://www.drscheme.org/index.html")
+              (string->url "http://www.drscheme.org/")
+              "index.html")
+  (test-c-u/r (string->url "http://www.drscheme.org/index.html")
+              (string->url "http://www.drscheme.org/")
+              "/index.html")
+  (test-c-u/r (string->url "http://www.drscheme.org/index.html")
+              (string->url "http://www.drscheme.org/a/b/c/")
+              "/index.html")
+  (test-c-u/r (string->url "http://www.drscheme.org/a/b/index.html")
+              (string->url "http://www.drscheme.org/a/b/c")
+              "index.html")
+  (test-c-u/r (string->url "http://www.drscheme.org/a/b/c/index.html")
+              (string->url "http://www.drscheme.org/a/b/c/")
+              "index.html")
+  (test-c-u/r (string->url "http://www.drscheme.org/a/b/d/index.html")
+              (string->url "http://www.drscheme.org/a/b/c")
+              "d/index.html")
+  (test-c-u/r (string->url "http://www.drscheme.org/a/b/c/d/index.html")
+              (string->url "http://www.drscheme.org/a/b/c/")
+              "d/index.html")
+  )
 
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;;