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)
if (QTest::qExec(&test1) != 0) {
        fInvalid = true;
    }
#if defined(ENABLE_WALLET) && defined(ENABLE_BIP70)
    PaymentServerTests test2;
    if (QTest::qExec(&test2) != 0) {
        fInvalid = true;
    }
#endif
    RPCNestedTests test3;
    if (QTest::qExec(&test3) != 0) {
        fInvalid = true;
    }
    CompatTests test4;
    if (QTest::qExec(&test4) != 0) {
        fInvalid = true;
    }
#ifdef ENABLE_WALLET
    WalletTests test5;
    if (QTest::qExec(&test5) != 0) {
        fInvalid = true;
    }
    AddressBookTests test6;
    if (QTest::qExec(&test6) != 0) {
        fInvalid = true;
    }
#endif
    return fInvalid;
}