diff --git a/test/main/plexus/core_test.clj b/test/main/plexus/core_test.clj
new file mode 100644
index 0000000..986d5d9
--- /dev/null
+++ b/test/main/plexus/core_test.clj
@@ -0,0 +1,62 @@
+(ns plexus.core-test
+  (:require
+   [clj-manifold3d.core :as m]
+   [clojure.test :as t]
+   [plexus.core :as p]))
+
+(defn get-volume [extrusion]
+  (-> extrusion
+      (p/get-model (:main-model extrusion))
+      (m/get-properties)
+      (:volume)))
+
+(def default-eps 0.002)
+
+(def pi Math/PI)
+(def pi|2 (/ pi 2))
+(def pi|3 (/ pi 3))
+(def pi|4 (/ pi 4))
+(def pow #(Math/pow %1 %2))
+
+(defn circle-area [r n]
+  (let [s (* 2 r (Math/sin (/ (* 2 pi) (* 2 n))))]
+    (/ (* n (pow s 2))
+       (* 4 (Math/tan (/ pi n))))))
+
+(defn about=
+  ([x y] (about= x y default-eps))
+  ([x y eps] (< (Math/abs (- x y)) eps)))
+
+(t/deftest test-extrudes
+  (t/is (about= (get-volume
+                 (p/extrude
+                  (p/frame :name :body :cross-section (m/square 10 10 true))
+                  (p/forward :length 10)))
+                1000.0))
+  (let [r 10
+        cr 100
+        cs 200]
+    (t/is (about= (get-volume
+                   (p/extrude
+                    (p/frame :name :body :cross-section (m/circle r cs))
+                    (p/left :angle (* 2 pi) :curve-radius cr :cs cs)))
+                  (* 2 (pow pi 2) (pow r 2) cr)
+                  200))
+    (t/is (about=
+           3180.828
+           (get-volume
+            (p/extrude
+             (p/result :name :tmp
+                       :expr (p/difference :body :mask))
+             (p/frame :name :body :cross-section (m/circle 4)
+                      :cs 30
+                      :curve-radius 30)
+             (p/frame :name :mask :cross-section (m/circle 3))
+             (for [i (range 4)]
+               (p/branch
+                :from :body
+                (case i
+                  0 (p/left :angle pi|2)
+                  1 (p/right :angle pi|2)
+                  2 (p/up :angle pi|2)
+                  3 (p/down :angle pi|2))))))))))