First attempt

tests/test_network.cpp

@@ -0,0 +1,56 @@
+#include <catch2/catch_test_macros.hpp>
+#include <kpn/kpn.hpp>
+#include <chrono>
+#include <thread>
+
+using namespace kpn;
+
+static int increment(int x) { return x + 1; }
+static int multiply2(int x) { return x * 2; }
+
+TEST_CASE("network build and run: linear pipeline", "[network]") {
+    // Nodes declared first — they own their input channels and must outlive the network
+    auto src = make_node<increment>(5);
+    auto dst = make_node<multiply2>(5);
+
+    auto& src_in = src.input_channel<0>();
+    Channel<int> final_out(5);
+    dst.set_output_channel<0>(&final_out);
+
+    Network net;
+    net.add("src", src)
+       .add("dst", dst)
+       .connect("src", src.output<0>(), "dst", dst.input<0>())
+       .build();
+
+    net.start();
+    src_in.push(5);           // 5 → increment → 6 → multiply2 → 12
+    int result = final_out.pop();
+    net.stop();
+
+    REQUIRE(result == 12);
+}
+
+TEST_CASE("network detects cycle", "[network]") {
+    auto a = make_node<increment>(5);
+    auto b = make_node<increment>(5);
+
+    Network net;
+    net.add("a", a).add("b", b);
+    net.connect("a", a.output<0>(), "b", b.input<0>());
+    net.connect("b", b.output<0>(), "a", a.input<0>());
+
+    REQUIRE_THROWS_AS(net.build(), NetworkCycleError);
+}
+
+TEST_CASE("stop disables input channels — producer push is silently dropped", "[network]") {
+    auto node = make_node<increment>(5);
+    auto& in_ch = node.input_channel<0>();
+
+    node.start();
+    node.stop();
+
+    // After stop, channel is disabled — push must not throw
+    in_ch.push(99);
+    REQUIRE(in_ch.size() == 0);
+}