[FEAT] Add a new identity test

tests/03_matrix.cpp

@@ -216,3 +216,14 @@ TEST_CASE("[Matrix] Transposing a matrix", "[Matrix]")
 
     REQUIRE(a == transposed);
 }
+
+/* ------------------------------------------------------------------------- */
+
+TEST_CASE("[Matrix] Transposing the identity matrix", "[Matrix]")
+{
+    Matrix a = Matrix::identity();
+
+    a.transpose();
+
+    REQUIRE(a == Matrix::identity());
+}