As of v0.18.1 I can use `test_bitcoin-qt -platform cocoa` to run GUI tests; this opens and closes a regtest GUI a bunch of times.

As of master (6e4f6553913978fcdddba30e0bb6f97edcb12e80) it seems to ignore the `-platform cocoa` and just run the test as with `minimal`.

As seen on macOS 10.14.6. Git bisect blames a2714a5c69f0b0506689af04c3e785f71ee0915d in #16578 `Do not pass in command line arguments to QApplication` (@achow101, @ryanofsky)
{
    TestChain100Setup test;
    auto chain = interfaces::MakeChain();
    std::shared_ptr<CWallet> wallet = std::make_shared<CWallet>(chain.get(), WalletLocation(), WalletDatabase::CreateMock());
    bool firstRun;
    wallet->LoadWallet(firstRun);
    auto build_address = [&wallet]() {
        CKey key;
        key.MakeNewKey(true);
        CTxDestination dest(GetDestinationForKey(
            key.GetPubKey(), wallet->m_default_address_type));
        return std::make_pair(dest, QString::fromStdString(EncodeDestination(dest)));
    };
    CTxDestination r_key_dest, s_key_dest;
    
    QString preexisting_r_address;
    QString r_label("already here (r)");
    
    QString preexisting_s_address;
    QString s_label("already here (s)");
    
    QString new_address;