`FormatMoney(CAmount n)` is not being properly defined for `n = std::numeric_limits<CAmount>::min()`. This is due to an invalid integer negation: the negation of `-9223372036854775808` cannot be represented in type `CAmount` (which has a max value of `9223372036854775807`):

https://github.com/bitcoin/bitcoin/blob/54f812d9d29893c690ae06b84aaeab128186aa36/src/util/moneystr.cpp#L12-L31

FWIW `FormatMoney(-9223372036854775808)` returns `--92233720368.-54775808` when compiled with UBSan (LLVM/Clang, `-fsanitize=undefined`).

Context: https://github.com/bitcoin/bitcoin/pull/20383#discussion_r523250890

It would be nice if `FormatMoney(CAmount n)` was properly defined for all `CAmount n` :)

These are the "expectations of least surprise":

```
BOOST_CHECK_EQUAL(FormatMoney(std::numeric_limits<CAmount>::max()), "92233720368.54775807");       //  9223372036854775807
BOOST_CHECK_EQUAL(FormatMoney(std::numeric_limits<CAmount>::max() - 1), "92233720368.54775806");   //  9223372036854775806
BOOST_CHECK_EQUAL(FormatMoney(std::numeric_limits<CAmount>::max() - 2), "92233720368.54775805");   //  9223372036854775805
BOOST_CHECK_EQUAL(FormatMoney(std::numeric_limits<CAmount>::max() - 3), "92233720368.54775804");   //  9223372036854775804
BOOST_CHECK_EQUAL(FormatMoney(std::numeric_limits<CAmount>::min() + 3), "-92233720368.54775805");  // -9223372036854775805
BOOST_CHECK_EQUAL(FormatMoney(std::numeric_limits<CAmount>::min() + 2), "-92233720368.54775806");  // -9223372036854775806
BOOST_CHECK_EQUAL(FormatMoney(std::numeric_limits<CAmount>::min() + 1), "-92233720368.54775807");  // -9223372036854775807
BOOST_CHECK_EQUAL(FormatMoney(std::numeric_limits<CAmount>::min()), "-92233720368.54775808");      // -9223372036854775808
```

These assertions are _guaranteed_ to hold for all cases above _except_ for the last one.
desc += arg;
            }
        }
        desc += "\n";
        out_sha.Write(MakeUCharSpan(desc));
        if (out_file) {
            BOOST_REQUIRE(fwrite(desc.data(), 1, desc.size(), out_file) == desc.size());
        }
    });
    if (out_file) {
        if (fclose(out_file)) throw std::system_error(errno, std::generic_category(), "fclose failed");
        out_file = nullptr;
    }
    unsigned char out_sha_bytes[CSHA256::OUTPUT_SIZE];
    out_sha.Finalize(out_sha_bytes);
    std::string out_sha_hex = HexStr(out_sha_bytes);
    
    
    
    
    
    
    
    
    
    BOOST_CHECK_EQUAL(out_sha_hex, "d1e436c1cd510d0ec44d5205d4b4e3bee6387d316e0075c58206cb16603f3d82");
}
struct ChainMergeTestingSetup : public BasicTestingSetup {
    static constexpr int MAX_ACTIONS = 2;
    enum Action { NONE, ENABLE_TEST, DISABLE_TEST, NEGATE_TEST, ENABLE_REG, DISABLE_REG, NEGATE_REG };