Refactor `AbstractSimpleTransportTestCase` and `MockTransportService` to not use `Version.transportVersion` 
test/framework/src/main/java/org/elasticsearch/transport/AbstractSimpleTransportTestCase.java
}
    public void testAcceptedChannelCount() throws Exception {
        assertBusy(() -> {
            TransportStats transportStats = serviceA.transport.getStats();
            assertEquals(channelsPerNodeConnection(), transportStats.getServerOpen());
        });
        assertBusy(() -> {
            TransportStats transportStats = serviceB.transport.getStats();
            assertEquals(channelsPerNodeConnection(), transportStats.getServerOpen());
        });
        serviceA.close();
        assertBusy(() -> {
            TransportStats transportStats = serviceB.transport.getStats();
            assertEquals(0, transportStats.getServerOpen());
        });
    }
    public void testTransportStatsWithException() throws Exception {
        MockTransportService serviceC = buildService("TS_C", version0, Settings.EMPTY);
        CountDownLatch receivedLatch = new CountDownLatch(1);
        CountDownLatch sendResponseLatch = new CountDownLatch(1);
        Exception ex = new RuntimeException("boom");
        ex.setStackTrace(new StackTraceElement[0]);
        serviceB.registerRequestHandler("internal:action", ThreadPool.Names.SAME, TestRequest::new, (request, channel, task) -> {
            
            threadPool.generic().execute(new AbstractRunnable() {
                @Override
                public void onFailure(Exception e) {
                    try {
                        channel.sendResponse(e);
                    } catch (IOException e1) {