diff --git a/test/geom/plane.cpp b/test/geom/plane.cpp
new file mode 100644
index 00000000..5f2d23fe
--- /dev/null
+++ b/test/geom/plane.cpp
@@ -0,0 +1,36 @@
+#include "geom/plane.hpp"
+#include "point.hpp"
+#include "tap.hpp"
+
+
+void
+test_distances (util::TAP::logger &tap)
+{
+    static struct {
+        util::point3f a, b, c;
+        util::point3f query;
+        float distance;
+        const char *message;
+    } const TESTS[] = {
+        { { 0, 0, 0 }, { 0, 1, 0 }, { 1, 0, 0 }, { 0, 0, 0 },  0, "colinear with plane about -z" },
+        { { 0, 0, 0 }, { 0, 1, 0 }, { 1, 0, 0 }, { 0, 0,-1 },  1, "in front of plane about -z" },
+        { { 0, 0, 0 }, { 0, 1, 0 }, { 1, 0, 0 }, { 0, 0, 1 }, -1, "behind plane about -z" },
+    };
+
+    for (auto const &t: TESTS) {
+        auto const p = util::geom::make_plane (t.a, t.b, t.c);
+        const auto d = distance (p, t.query);
+        tap.expect_eq (d, t.distance, "%!", t.message);
+    }
+};
+
+
+int
+main (int, char**)
+{
+    util::TAP::logger tap;
+
+    test_distances (tap);
+
+    return tap.status ();
+}
\ No newline at end of file