Added some comments on the test setup

Author: feniup

tests/unit/mainTest.ml

@@ -22,4 +22,4 @@ let subset_tests = "" >::: [SparseMatrixImplementationTest.tests]
 let () =
   print_string "\027[0;1munit: \027[0;0;00m";
   run_test_tt_main subset_tests (* Remove this and uncomment the line below to run all tests.*)
- (* run_test_tt_main all_tests *)
+(* run_test_tt_main all_tests *)