This is tough

unit-tests/matrix-tests.cpp

@@ -539,13 +539,13 @@ TEST_CASE("QR Decompositions", "Matrix") {
     }
 
     // Check that Qᵀ * Q ≈ I
-    // This MUST be true even if the rank of A is 2 because without this,
-    // calculating eigenvalues/vectors will not work.
+    // Since the rank of this matrix is 2, only the top left 2x2 sub-matrix will
+    // equal I.
     Matrix<3, 3> Qt = Q.Transpose();
     Matrix<3, 3> QtQ{};
     QtQ = Qt * Q;
-    for (int i = 0; i < 3; ++i) {
-      for (int j = 0; j < 3; ++j) {
+    for (int i = 0; i < 2; ++i) {
+      for (int j = 0; j < 2; ++j) {
         if (i == j)
           REQUIRE_THAT(QtQ[i][j], Catch::Matchers::WithinRel(1.0f, 1e-4f));
         else