Got the matrix library compiling in the tests

unit-tests/matrix-tests.cpp

@@ -1,5 +1,9 @@
+// include the unit test framework first
 #include <catch2/catch_test_macros.hpp>
 
+// include the module you're going to test next
+#include "Matrix.hpp"
+
 unsigned int Factorial(unsigned int number) {
   return number <= 1 ? number : Factorial(number - 1) * number;
 }