eliminated unused headers test_add.hpp, test_subtract.hp, etc.

The code in these haaders has been moved into test_add.cpp, test_subtract.cpp, etc.

test/test_checked.cpp

@@ -9,9 +9,6 @@
 #include <iostream>
 #include <cassert>
 
-// don't use constexpr so we can debug
-#define SAFE_NUMERIC_CONSTEXPR constexpr
-
 #include "../include/checked_result.hpp"
 #include "../include/checked.hpp"
 
@@ -78,6 +75,10 @@ bool test_add(
 #include "test.hpp"
 #include "test_values.hpp"
 
+// note: same test matrix as used in test_add.  Here we test all combinations
+// safe and unsafe integers.  in test_checked we test all combinations of
+// integer primitives
+
 const char *test_addition_result[VALUE_ARRAY_SIZE] = {
 //      0       0       0       0
 //      01234567012345670123456701234567