Added the beginnings of interop tests

This demonstrates that the idea of naming Lisp 1.5 functions implemented
in Clojure with all-upper names will not work with the present INTEROP
operator, so some rethink is going to be needed.

test/beowulf/interop_test.clj

@@ -0,0 +1,18 @@
+(ns beowulf.interop-test
+  (:require [clojure.test :refer :all]
+            [beowulf.cons-cell :refer [make-beowulf-list make-cons-cell NIL T F]]
+            [beowulf.bootstrap :refer [EVAL INTEROP]]
+            [beowulf.host :refer :all]
+            [beowulf.read :refer [gsp]]))
+
+
+(deftest interop-test
+  (testing "INTEROP called from Clojure"
+    (let [expected '123
+          actual (INTEROP (gsp "(CLOJURE CORE STR)") (gsp "(1 2 3)"))]
+      (is (= actual expected))))
+  (testing "INTEROP called from Lisp"
+    (let [expected 'ABC
+          actual (EVAL (gsp "(INTEROP '(CLOJURE CORE STR) '('A 'B 'C)"))]
+      (is (= actual expected))))
+    )