Test zero-delay sender wakeups and failure injection

tests/Makefile.am

@@ -1013,7 +1013,7 @@ test_etcp_session_LDFLAGS = $(test_clock_ldflags)
 test_etcp_windows_SOURCES = test_etcp_windows.c $(test_clock_sources)
 test_etcp_windows_LDADD = $(LIBUTUN) $(COMMON_LIBS)
 test_etcp_windows_LDFLAGS = $(test_clock_ldflags) -Wl,--wrap=etcp_encrypt_send -Wl,--wrap=memory_pool_alloc_impl \
-    -Wl,--wrap=bbr_main -Wl,--wrap=uasync_set_timeout
+    -Wl,--wrap=bbr_main -Wl,--wrap=uasync_set_timeout -Wl,--wrap=uasync_call_soon
 
 test_etcp_router_tcp_SOURCES = test_etcp_router_tcp.c
 test_etcp_router_tcp_LDADD = $(LIBUTUN) $(COMMON_LIBS)

tests/test_etcp_windows.c

@@ -299,6 +299,14 @@ static void timer_failure(void) {
     etcp_conn_ref_free(conn); teardown();
 }
 
+static void immediate_send(void) {
+    setup(); enqueue(100);
+    CHECK(conn->tx_token && !conn->tx_delayed);
+    uasync_drain_immediate(ua);
+    CHECK(sends == 1 && conn->input_wait_ack->count == 1);
+    ack_all(); teardown();
+}
+
 int main(void) {
     debug_config_init(); debug_set_level(DEBUG_LEVEL_ERROR);
     if (getenv("UTUN_TEST_DEBUG")) debug_set_category_level(DEBUG_CATEGORY_ETCP, DEBUG_LEVEL_DEBUG);
@@ -306,7 +314,7 @@ int main(void) {
     size_t baseline = u_get_allocated_count();
     void (*cases[])(void) = {selection, boundaries_ack_burst, late_ack_and_migration, lost_ack_and_shrink,
         grow_and_session, allocation_and_send_failure, removed_link_and_bbr, pacing_reset_close, initial_readiness,
-        config_limits, timer_failure};
+        config_limits, timer_failure, immediate_send};
     for (unsigned i = 0; i < sizeof(cases) / sizeof(cases[0]); i++) {
         cases[i](); CHECK(u_get_allocated_count() == baseline);
         DEBUG_INFO(DEBUG_CATEGORY_DEBUG, "PASS ETCP window scenario %u", i);