Create a unit test system

Setup cantedraw/tests with a test-system record, as well as linking it
back to cantedraw so we can run test-system on cantedraw and run the
tests.

Using parachute, we can setup a suite of unit tests for each package.
For each package in src/ or lib/ we'll write a separate unit test
suite with tests for all the public exposing functionality.

I've setup a main suite in cantedraw/tests/main which will depend on
each of the unit test suites so we can run the tests all at once.

Currently we have one test for the --> macro.

cantedraw.asd

@@ -2,6 +2,7 @@
   :author "Aryadev Chavali <aryadev@aryadevchavali.com>"
   :license "GPL-2"
   :depends-on (:alexandria)
+  :in-order-to ((asdf:test-op (asdf:test-op :cantedraw/tests)))
   :components ((:file "packages")
                (:module "lib"
                 :components
@@ -17,6 +18,22 @@
   :build-pathname "bin/cantedraw"
   :entry-point "cantedraw.main:start")
 
+(asdf:defsystem "cantedraw/tests"
+  :author "Aryadev Chavali <aryadev@aryadevchavali.com>"
+  :license "GPL-2"
+  :depends-on (:cantedraw
+               :parachute)
+  :components ((:module "tests"
+                :components
+                ((:file "macros")
+                 ;; (:file "functions")
+                 ;; (:file "model")
+                 ;; (:file "player")
+                 ;; (:file "game")
+                 (:file "main"))))
+  :perform (test-op (op c) (uiop:symbol-call :parachute :test
+                                             :cantedraw/tests/main)))
+
 ;; Compress image for smaller binary size.
 #+nil
 (defmethod asdf:perform ((o asdf:image-op) (c asdf:system))