diff --git a/src/stereographic_extrude.scad b/src/stereographic_extrude.scad
index 2b4e16b9..efd57169 100644
--- a/src/stereographic_extrude.scad
+++ b/src/stereographic_extrude.scad
@@ -32,4 +32,12 @@ module stereographic_extrude(shadow_side_leng) {
         linear_extrude(outer_sphere_r * 2, scale = 0.01) 
             children();
     }
+
+    // hook for testing
+    test_stereographic_extrude_rs(outer_sphere_r, inner_sphere_r);
+}
+
+// override for testing
+module test_stereographic_extrude_rs(outer_sphere_r, inner_sphere_r) {
+
 }
\ No newline at end of file
diff --git a/test/test_all.scad b/test/test_all.scad
index 07d5f21b..c49cfe73 100644
--- a/test/test_all.scad
+++ b/test/test_all.scad
@@ -39,6 +39,7 @@ include <test_sphere_spiral.scad>;
 
 // Extrude
 include <test_ellipse_extrude.scad>;
+include <test_stereographic_extrude.scad>;
 
 // 2D Shape
 include <test_shape_arc.scad>;
diff --git a/test/test_stereographic_extrude.scad b/test/test_stereographic_extrude.scad
new file mode 100644
index 00000000..fa284aaa
--- /dev/null
+++ b/test/test_stereographic_extrude.scad
@@ -0,0 +1,22 @@
+include <unittest.scad>;
+
+module test_stereographic_extrude() {
+    echo("==== test_stereographic_extrude ====");
+
+    include <stereographic_extrude.scad>;
+
+    module test_stereographic_extrude_rs(outer_sphere_r, inner_sphere_r) {
+        assertEqualPoint([16.6667, 15.0756], [outer_sphere_r, inner_sphere_r]);
+    }
+    
+    dimension = 100;
+
+    stereographic_extrude(shadow_side_leng = dimension)
+       text(
+            "M", size = dimension, 
+            valign = "center", halign = "center"
+       );
+
+}
+
+test_stereographic_extrude();
\ No newline at end of file