itest: add integrated-mode fail-fast test for tapd startup errors

Author: ffranr

itest/litd_mode_integrated_test.go

@@ -465,6 +465,38 @@ func testModeIntegrated(ctx context.Context, net *NetworkHarness,
 	)
 }
 
+// testCriticalTapStartupFailure ensures LiT exits quickly when a critical
+// integrated sub-server (tapd) fails to start during boot.
+func testCriticalTapStartupFailure(ctx context.Context, net *NetworkHarness,
+	t *harnessTest) {
+
+	// Force tapd to bind to an invalid port to guarantee a startup failure
+	// in integrated mode.
+	node, err := net.NewNode(
+		t.t, "FailFastTap", nil, false, false,
+		"--taproot-assets.rpclisten=127.0.0.1:65536",
+	)
+	require.NoError(t.t, err)
+
+	defer func() {
+		_ = net.ShutdownNode(node)
+	}()
+
+	select {
+	case procErr := <-net.ProcessErrors():
+		require.ErrorContains(t.t, procErr, "invalid port")
+	case <-time.After(15 * time.Second):
+		t.Fatalf("expected tapd startup failure to be reported")
+	}
+
+	// LiT should terminate promptly after the critical startup failure.
+	select {
+	case <-node.processExit:
+	case <-time.After(5 * time.Second):
+		t.Fatalf("litd did not exit after tapd startup failure")
+	}
+}
+
 // integratedTestSuite makes sure that in integrated mode all daemons work
 // correctly.
 func integratedTestSuite(ctx context.Context, net *NetworkHarness, t *testing.T,

itest/litd_test_list_on_test.go

@@ -87,6 +87,11 @@ var allTestCases = []*testCase{
 		test:       testCustomChannelsHtlcForceCloseMpp,
 		noAliceBob: true,
 	},
+	{
+		name:       "critical tap startup failure",
+		test:       testCriticalTapStartupFailure,
+		noAliceBob: true,
+	},
 	{
 		name:       "custom channels balance consistency",
 		test:       testCustomChannelsBalanceConsistency,