For problem 3 (and 5), what's an easy way to flip my test routine between testing a Set of std::string and a Set of unsigned long?

Here's one technique that lets you flip by commenting out or uncommenting just one line in testSet.cpp:

    #include "Set.h"
    #include <iostream>
    #include <cassert>
    using namespace std;

    // To test a Set of unsigned long, leave the #define line commented out;
    // to test a Set of string, remove the "//".

    // #define TEST_WITH_STRING

    #ifdef TEST_WITH_STRING

    const ItemType DUMMY_VALUE = "hello";
    const ItemType V1 = "abc";

    #else // assume unsigned long

    const ItemType DUMMY_VALUE = 9876543;
    const ItemType V1 = 123456789;

    #endif

    void test()
    {
        Set s;
        assert(s.empty());
        ItemType v = DUMMY_VALUE;
        assert( !s.get(0, v)  &&  v == DUMMY_VALUE); // v unchanged by get failure
        s.insert(V1);
        assert(s.size() == 1);
        assert(s.get(0, v)  &&  v == V1);
    }

    int main()
    {
        test();
        cout << "Passed all tests" << endl;
    }

When your Set.h has ItemType being a type alias for std::string, then by making the symbol TEST_WITH_STRING defined, the #ifdef will select the code that initializes the constants DUMMY_VALUE and V1 in a way that is consistent with the Set. Similarly, if the type alias specifies unsigned long, you would comment out the #define of TEST_WITH_STRING; this would cause the #ifdef to select the #else part, which initializes the constants appropriately for that kind of Set.

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	W1 W2 W3 W4 W5 W6
	B1 B2 B3 B4 B5 B6

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	B1 B2 B3 B4 B5 B6
	W1 W2 W3 W4 W5 W6

Yes.