diff --git a/t-lack.asd b/t-lack.asd
index df6876e..7391025 100644
--- a/t-lack.asd
+++ b/t-lack.asd
@@ -15,7 +15,7 @@
                :prove)
   :components ((:module "t"
                 :components
-                ((:test-file "lack"))))
+                ((:test-file "builder"))))
 
   :defsystem-depends-on (:prove-asdf)
   :perform (test-op :after (op c)
diff --git a/t/builder.lisp b/t/builder.lisp
new file mode 100644
index 0000000..5be4df5
--- /dev/null
+++ b/t/builder.lisp
@@ -0,0 +1,50 @@
+(in-package :cl-user)
+(defpackage t.lack.builder
+  (:use :cl
+        :prove
+        :lack.builder))
+(in-package :t.lack.builder)
+
+(plan 8)
+
+(defvar *app*
+  (lambda (env)
+    (declare (ignore env))
+    '(200 (:content-type "text/html") ("ok from app"))))
+
+(is-type (builder (lambda (app)
+                    (lambda (env)
+                      (funcall app env)))
+                  *app*)
+         'function
+         "builder")
+
+(is-type (builder
+          (if t
+              (lambda (app)
+                (lambda (env)
+                  (funcall app env)))
+              nil)
+          *app*)
+         'function
+         "Can embed CL code")
+
+(is-type (builder nil (if t nil nil) nil *app*)
+         'function
+         "NIL is ignored")
+
+(let ((mount-app (builder
+                  (:mount "/admin" (lambda (env) `(200 () ("admin" ,(getf env :path-info)))))
+                  *app*)))
+  (is (nth 2 (funcall mount-app '(:path-info "/login")))
+      '("ok from app"))
+  (is (nth 2 (funcall mount-app '(:path-info "/admin/login")))
+      '("admin" "/login"))
+  (is (nth 2 (funcall mount-app '(:path-info "/admin")))
+      '("admin" "/"))
+  (is (nth 2 (funcall mount-app '(:path-info "/admin/")))
+      '("admin" "/"))
+  (is (nth 2 (funcall mount-app '(:path-info "/administrators")))
+      '("ok from app")))
+
+(finalize)
diff --git a/t/lack.lisp b/t/lack.lisp
deleted file mode 100644
index 8e5bd5d..0000000
--- a/t/lack.lisp
+++ /dev/null
@@ -1,14 +0,0 @@
-(in-package :cl-user)
-(defpackage t.lack
-  (:use :cl
-        :lack
-        :prove))
-(in-package :t.lack)
-
-;; NOTE: To run this test file, execute `(asdf:test-system :lack)' in your Lisp.
-
-(plan nil)
-
-;; blah blah blah.
-
-(finalize)