diff --git a/src/math/vec4.h b/src/math/vec4.h
index a5db4b1..c6ccc32 100644
--- a/src/math/vec4.h
+++ b/src/math/vec4.h
@@ -22,13 +22,13 @@ inline static Vec4f_t vec4f_clone(const Vec4f_t *__restrict v)
     return *v;
 }
 
-Vec4f_t vec4f_add_r(Vec4f_t *__restrict out, Vec4f_t a);
+Vec4f_t* vec4f_add_r(Vec4f_t *__restrict out, Vec4f_t a);
 Vec4f_t vec4f_add(Vec4f_t a, Vec4f_t b);
 
-Vec4f_t vec4f_sub_r(Vec4f_t *__restrict out, Vec4f_t a);
+Vec4f_t* vec4f_sub_r(Vec4f_t *__restrict out, Vec4f_t a);
 Vec4f_t vec4f_sub(Vec4f_t a, Vec4f_t b);
 
-Vec4f_t vec4f_scale_r(Vec4f_t *__restrict out, float scale);
+Vec4f_t* vec4f_scale_r(Vec4f_t *__restrict out, float scale);
 Vec4f_t vec4f_scale(Vec4f_t a, float scale);
 
 float vec4f_dot(Vec4f_t a, Vec4f_t b);
@@ -38,10 +38,10 @@ inline static float vec4f_len(Vec4f_t v)
     return sqrtf(vec4f_dot(v, v));
 }
 
-Vec4f_t vec4f_norm_r(Vec4f_t *__restrict v);
+Vec4f_t* vec4f_norm_r(Vec4f_t *__restrict v);
 Vec4f_t vec4f_norm(Vec4f_t v);
 
-Vec4f_t vec4f_lerp_r(Vec4f_t *__restrict a, Vec4f_t b, float t);
+Vec4f_t* vec4f_lerp_r(Vec4f_t *__restrict a, Vec4f_t b, float t);
 Vec4f_t vec4f_lerp(Vec4f_t a, Vec4f_t b, float t);
 
 float vec4f_angle(Vec4f_t a, Vec4f_t b);
diff --git a/tests/test_vec4f.c b/tests/test_vec4f.c
index f8cc217..4ea7037 100644
--- a/tests/test_vec4f.c
+++ b/tests/test_vec4f.c
@@ -19,6 +19,9 @@ void test_vec4f_creation() {
     assert(fabsf(v.w - 4.f) < EPSILON);
 }
 
+// a -> [1, 2, 3, 4]
+// b -> [5, 6, 7, 8]
+// r -> [6, 8, 10, 12]
 void test_vec4f_add() {
     Vec4f_t a = vec4f(1.f, 2.f, 3.f, 4.f);
     Vec4f_t b = vec4f(5.f, 6.f, 7.f, 8.f);
@@ -29,6 +32,9 @@ void test_vec4f_add() {
     assert(fabsf(r.w - 12.f) < EPSILON);
 }
 
+// a -> [5, 6, 7, 8]
+// b -> [1, 2, 3, 4]
+// r -> [4, 4, 4, 4]
 void test_vec4f_sub() {
     Vec4f_t a = vec4f(5.f, 6.f, 7.f, 8.f);
     Vec4f_t b = vec4f(1.f, 2.f, 3.f, 4.f);
@@ -39,7 +45,8 @@ void test_vec4f_sub() {
     assert(fabsf(r.z - 4.f) < EPSILON);
     assert(fabsf(r.w - 4.f) < EPSILON);
 }
-
+// a -> [1, 2, 3, 4]
+// r -> [2, 4, 6, 8]
 void test_vec4f_scale() {
     Vec4f_t a = vec4f(1.f, 2.f, 3.f, 4.f);
     Vec4f_t r = vec4f_scale(a, 2.f);
@@ -49,11 +56,99 @@ void test_vec4f_scale() {
     assert(fabsf(r.w - 8.f) < EPSILON);
 }
 
+// dot product:
+//      + : same direction
+//      0 : orthgonal
+//      - : opposite direction
+void test_vec4f_dot() {
+    Vec4f_t a = vec4f(1.f, 2.f, 3.f, 4.f);
+    Vec4f_t b = vec4f(5.f, 6.f, 7.f, 8.f);
+    float d = vec4f_dot(a, b);
+    assert(fabsf(d - (1*5 + 2*6 + 3*7 + 4*8)) < EPSILON);
+}
+
+// normalize:
+//      [4, 0, 0, 0] -> [1, 0, 0, 0]
+void test_vec4f_norm() {
+    Vec4f_t v = vec4f(3.f, 0.f, 0.f, 0.f);
+    Vec4f_t n = vec4f_norm(v);
+    assert(fabsf(n.x - 1.f) < EPSILON);
+    assert(fabsf(n.y) < EPSILON);
+    assert(fabsf(n.z) < EPSILON);
+    assert(fabsf(n.w) < EPSILON);
+}
+
+// lerp:
+//      return vector between a and b
+//      if t = 0.5
+//         a = [0, 0, 0, 0]
+//         b = [3, 3, 3, 3]
+//         r = [1.5, 1.5, 1.5, 1.5] (t = 0.5) is middle
+void test_vec4f_lerp() {
+    Vec4f_t a = vec4f(0.f, 0.f, 0.f, 0.f);
+    Vec4f_t b = vec4f(1.f, 1.f, 1.f, 1.f);
+    Vec4f_t r = vec4f_lerp(a, b, 0.5f);
+    assert(fabsf(r.x - 0.5f) < EPSILON);
+    assert(fabsf(r.y - 0.5f) < EPSILON);
+    assert(fabsf(r.z - 0.5f) < EPSILON);
+    assert(fabsf(r.w - 0.5f) < EPSILON);
+}
+
+// angle:
+//      return angle of two vectors
+void test_vec4f_angle() {
+    Vec4f_t a = vec4f(1.f, 0.f, 0.f, 0.f);
+    Vec4f_t b = vec4f(0.f, 1.f, 0.f, 0.f);
+    float angle = vec4f_angle(a, b);
+    assert(fabsf(angle - (float)(M_PI / 2)) < EPSILON);
+}
+
+// proj:
+//      return size of a on b 
+void test_vec4f_proj() {
+    Vec4f_t a = vec4f(2.f, 0.f, 0.f, 0.f);
+    Vec4f_t b = vec4f(1.f, 0.f, 0.f, 0.f);
+    Vec4f_t r = vec4f_proj(a, b);
+    assert(fabsf(r.x - 2.f) < EPSILON);
+    assert(fabsf(r.y) < EPSILON);
+    assert(fabsf(r.z) < EPSILON);
+    assert(fabsf(r.w) < EPSILON);
+}
+
+// refl:
+//      return a bounce vector
+//      raytracing
+void test_vec4f_refl() {
+    Vec4f_t v = vec4f(1.f, -1.f, 0.f, 0.f);
+    Vec4f_t normal = vec4f(0.f, 1.f, 0.f, 0.f);
+    Vec4f_t r = vec4f_refl(v, normal);
+    assert(fabsf(r.x - 1.f) < EPSILON);
+    assert(fabsf(r.y - 1.f) < EPSILON);
+    assert(fabsf(r.z) < EPSILON);
+    assert(fabsf(r.w) < EPSILON);
+}
+
+// dist:
+//      return distance between two vectors
+void test_vec4f_dist() {
+    Vec4f_t a = vec4f(1.f, 0.f, 0.f, 0.f);
+    Vec4f_t b = vec4f(0.f, 0.f, 0.f, 0.f);
+    float d = vec4f_dist(a, b);
+    assert(fabsf(d - 1.f) < EPSILON);
+}
+
 void run_all_tests() {
     test_vec4f_creation();
     test_vec4f_add();
     test_vec4f_sub();
     test_vec4f_scale();
+    test_vec4f_dot();
+    test_vec4f_norm();
+    test_vec4f_lerp();
+    test_vec4f_angle();
+    test_vec4f_proj();
+    test_vec4f_refl();
+    test_vec4f_dist();
 }
 
 int main(void) {
diff --git a/tests/unity b/tests/unity
deleted file mode 160000
index b9d897b..0000000
--- a/tests/unity
+++ /dev/null
@@ -1 +0,0 @@
-Subproject commit b9d897b5f38674248c86fb58342b87cb6006fe1f