diff --git a/Makefile b/Makefile
index 9452c5f..d02f502 100644
--- a/Makefile
+++ b/Makefile
@@ -12,6 +12,7 @@ OBJS=Implicit.o \
 	 util/ObjParser.o \
 	 MarchingCubes.o \
 	 _gen/marching_cubes_data.o \
+	 tests/TestImplicitSphere.o \
 	 render/GlutRender.o
 
 all: $(TARGETS:=.bin)
diff --git a/main_test_sphere.cpp b/main_test_sphere.cpp
new file mode 100644
index 0000000..61fb823
--- /dev/null
+++ b/main_test_sphere.cpp
@@ -0,0 +1,33 @@
+/** An entry-point file using render/GlutRender as a renderer, displaying a
+ * simple sphere.
+ **/
+
+#include "render/GlutRender.hpp"
+#include "util/ObjParser.hpp"
+#include "tests/TestImplicitSphere.hpp"
+#include "Mesh.hpp"
+#include "MarchingCubes.hpp"
+
+int main(int argc, char** argv) {
+    GlutRender& render = GlutRender::get_instance();
+    render.init(&argc, argv, 640, 480, "Bouncing stuff");
+
+    TestImplicitSphere sph1(Point(2.5, -1, 0), 1);
+    TestImplicitSphere sph2(Point(-4, 0.5, 0), 1.4);
+    Mesh m_sph1 = MarchingCubes(sph1,
+            Cuboid(Point(1, -2, -2), Point(3, 0, 2)))();
+    Mesh m_sph2 = MarchingCubes(sph2,
+            Cuboid(Point(-6, -2, -2), Point(2, 3, 2)))();
+    render.add_mesh(&m_sph1);
+    render.add_mesh(&m_sph2);
+
+    puts("=== All set! ===");
+
+    printf("Sph1 has %ld vertices, %ld faces.\n",
+            m_sph1.get_vertices().size(),
+            m_sph1.get_faces().size());
+
+    render.run();
+
+    return 0;
+}
diff --git a/tests/TestImplicitSphere.cpp b/tests/TestImplicitSphere.cpp
new file mode 100644
index 0000000..575dc56
--- /dev/null
+++ b/tests/TestImplicitSphere.cpp
@@ -0,0 +1,9 @@
+#include "TestImplicitSphere.hpp"
+
+double TestImplicitSphere::operator()(double x, double y, double z) const {
+    auto sq = [](double x) { return x*x; };
+    return - (sq(center.x - x)
+            + sq(center.y - y)
+            + sq(center.z - z))
+        + sq(radius);
+}
diff --git a/tests/TestImplicitSphere.hpp b/tests/TestImplicitSphere.hpp
new file mode 100644
index 0000000..09b1fb9
--- /dev/null
+++ b/tests/TestImplicitSphere.hpp
@@ -0,0 +1,14 @@
+#pragma once
+
+#include "../Implicit.hpp"
+
+class TestImplicitSphere: public ImplicitSurface {
+    public:
+        TestImplicitSphere(const Point& center, double r):
+            center(center), radius(r) {}
+        virtual double operator()(double x, double y, double z) const;
+
+    private:
+        Point center;
+        double radius;
+};