quaternion: add test for from_euler

test/quaternion.cpp

@@ -131,5 +131,24 @@ main (void)
         }
     }
 
+    {
+        static struct {
+            float x, y, z;
+            cruft::quaternionf expected;
+            char const *msg;
+        } const TESTS[] = {
+            { 1.f, 2.f, 3.f, { -0.3688714f, 0.7549338f, -0.2061492f, 0.5015091f, }, "positive rotation", },
+        };
+
+        for (auto const &t: TESTS) {
+            tap.expect_eq (
+                cruft::quaternionf::from_euler ({ t.x, t.y, t.z }),
+                t.expected,
+                "from_euler: %!",
+                t.msg
+            );
+        }
+    }
+
     return tap.status ();
 }