Test all 6 ways that triangle intersection can return false using a simplified method (one triangle is a point) to avoid complication.

math/test/common_test.cxx

@@ -254,14 +254,19 @@ TEST(TriangleTest, TriangleIntersectsSelf) {
 
 TEST(TriangleTest, DoesNotIntersectOffset) {
   triangle lhs{{{0, 0}}, {{0, 1}}, {{1, 0}}};
-  triangle rhs{{{-1, -1}}, {{-1, 0}}, {{0, -1}}};
-  EXPECT_FALSE(math::intersects(lhs, rhs));
-}
-
-TEST(TriangleTest, DoesNotIntersectOffset2) {
-  triangle lhs{{{0, 0}}, {{0, 1}}, {{1, 0}}};
-  triangle rhs{{{1, 1}}, {{1, 2}}, {{2, 1}}};
-  EXPECT_FALSE(math::intersects(lhs, rhs));
+  auto tri = [](math::dim2::point const & pt) {
+    return triangle{pt, pt, pt};
+  };
+  math::dim2::point const clock_ab{{1, 1}};
+  math::dim2::point const clock_bc{{-1, -1}};
+  math::dim2::point const clock_ca{{-1, 2}};
+
+  EXPECT_FALSE(math::intersects(lhs, tri(clock_ab)));
+  EXPECT_FALSE(math::intersects(tri(clock_ab), lhs));
+  EXPECT_FALSE(math::intersects(lhs, tri(clock_bc)));
+  EXPECT_FALSE(math::intersects(tri(clock_bc), lhs));
+  EXPECT_FALSE(math::intersects(lhs, tri(clock_ca)));
+  EXPECT_FALSE(math::intersects(tri(clock_ca), lhs));
 }
 
 TEST(RotateTest, RotatingSquareAroundOrigin) {