diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index a2fc7f7..5a741b0 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -47,6 +47,8 @@ target_include_directories(netft_posix_transport PRIVATE
 )
 target_link_options(netft_posix_transport PRIVATE
   "-Wl,--wrap=poll"
+  "-Wl,--wrap=recv"
+  "-Wl,--wrap=send"
 )
 target_link_libraries(netft_posix_transport PRIVATE ${NETFT_GTEST_MAIN_TARGET})
 
@@ -140,3 +142,21 @@ target_link_libraries(netft_cli_test PRIVATE
 add_dependencies(netft_cli_test netft_cli)
 
 add_test(NAME netft_cli COMMAND netft_cli_test)
+
+add_test(
+  NAME netft_cli_help
+  COMMAND ${CMAKE_COMMAND}
+    -DPROGRAM=$<TARGET_FILE:netft_cli>
+    -DEXPECTED_EXIT_CODE=0
+    -DARGUMENTS=--help
+    -P ${CMAKE_CURRENT_SOURCE_DIR}/assert_exit_code.cmake
+)
+
+add_test(
+  NAME netft_cli_invalid_command
+  COMMAND ${CMAKE_COMMAND}
+    -DPROGRAM=$<TARGET_FILE:netft_cli>
+    -DEXPECTED_EXIT_CODE=2
+    -DARGUMENTS=invalid-command
+    -P ${CMAKE_CURRENT_SOURCE_DIR}/assert_exit_code.cmake
+)
diff --git a/test/assert_exit_code.cmake b/test/assert_exit_code.cmake
new file mode 100644
index 0000000..c350247
--- /dev/null
+++ b/test/assert_exit_code.cmake
@@ -0,0 +1,23 @@
+if(NOT DEFINED PROGRAM OR NOT DEFINED EXPECTED_EXIT_CODE)
+  message(FATAL_ERROR "PROGRAM and EXPECTED_EXIT_CODE are required")
+endif()
+
+execute_process(
+  COMMAND "${PROGRAM}" ${ARGUMENTS}
+  TIMEOUT 30
+  RESULT_VARIABLE actual_exit_code
+  OUTPUT_QUIET
+  ERROR_QUIET
+)
+
+if(NOT "${actual_exit_code}" MATCHES "^-?[0-9]+$")
+  message(FATAL_ERROR
+    "Failed to execute ${PROGRAM}: ${actual_exit_code}"
+  )
+endif()
+
+if(NOT actual_exit_code EQUAL EXPECTED_EXIT_CODE)
+  message(FATAL_ERROR
+    "Expected exit code ${EXPECTED_EXIT_CODE}, got ${actual_exit_code}"
+  )
+endif()
diff --git a/test/test_posix_transport.cpp b/test/test_posix_transport.cpp
index 782c684..aa4a9a4 100644
--- a/test/test_posix_transport.cpp
+++ b/test/test_posix_transport.cpp
@@ -3,11 +3,14 @@
 #include <gtest/gtest.h>
 
 #include <poll.h>
+#include <sys/socket.h>
 
+#include <algorithm>
 #include <array>
 #include <cerrno>
 #include <chrono>
 #include <cstdint>
+#include <limits>
 #include <stdexcept>
 #include <thread>
 #include <vector>
@@ -16,42 +19,99 @@ namespace {
 
 using namespace std::chrono_literals;
 
-enum class PollBehavior { RepeatedEintrThenTimeout, EintrPastDeadline, Error };
+enum class PollBehavior {
+  RepeatedEintrThenTimeout,
+  EintrPastDeadline,
+  Error,
+  InvalidDescriptor,
+  Readable,
+  Timeout
+};
+enum class SendBehavior { Complete, Error, ShortWrite };
+enum class ReceiveBehavior { Payload, Interrupted, Error };
 
 constexpr int kInterruptCount = 3;
 std::vector<int> poll_timeouts;
 int poll_calls{};
 PollBehavior poll_behavior{PollBehavior::RepeatedEintrThenTimeout};
+SendBehavior send_behavior{SendBehavior::Complete};
+ReceiveBehavior receive_behavior{ReceiveBehavior::Payload};
+
+void reset_behaviors() {
+  poll_timeouts.clear();
+  poll_calls = 0;
+  poll_behavior = PollBehavior::RepeatedEintrThenTimeout;
+  send_behavior = SendBehavior::Complete;
+  receive_behavior = ReceiveBehavior::Payload;
+}
 
 } // namespace
 
-extern "C" int __wrap_poll(pollfd *, nfds_t, const int timeout) {
+extern "C" int __wrap_poll(pollfd *descriptors, const nfds_t count, const int timeout) {
   poll_timeouts.push_back(timeout);
-  if (poll_behavior == PollBehavior::Error) {
+  switch (poll_behavior) {
+  case PollBehavior::Error:
     errno = EBADF;
     return -1;
-  }
-  if (poll_behavior == PollBehavior::EintrPastDeadline) {
+  case PollBehavior::InvalidDescriptor:
+    if (count > 0) {
+      descriptors[0].revents = POLLNVAL;
+    }
+    return 1;
+  case PollBehavior::Readable:
+    if (count > 0) {
+      descriptors[0].revents = POLLIN;
+    }
+    return 1;
+  case PollBehavior::Timeout:
+    return 0;
+  case PollBehavior::EintrPastDeadline:
     if (poll_calls++ == 0) {
       std::this_thread::sleep_for(std::chrono::milliseconds{timeout} + 10ms);
       errno = EINTR;
       return -1;
     }
     return 0;
+  case PollBehavior::RepeatedEintrThenTimeout:
+    if (poll_calls++ < kInterruptCount) {
+      std::this_thread::sleep_for(10ms);
+      errno = EINTR;
+      return -1;
+    }
+    std::this_thread::sleep_for(std::chrono::milliseconds{timeout});
+    return 0;
   }
-  if (poll_calls++ < kInterruptCount) {
-    std::this_thread::sleep_for(10ms);
-    errno = EINTR;
+  return 0;
+}
+
+extern "C" ssize_t __wrap_send(int, const void *, const std::size_t length, int) {
+  if (send_behavior == SendBehavior::Error) {
+    errno = EIO;
     return -1;
   }
+  if (send_behavior == SendBehavior::ShortWrite) {
+    return static_cast<ssize_t>(length - 1);
+  }
+  return static_cast<ssize_t>(length);
+}
 
-  std::this_thread::sleep_for(std::chrono::milliseconds{timeout});
-  return 0;
+extern "C" ssize_t __wrap_recv(int, void *data, const std::size_t length, int) {
+  if (receive_behavior == ReceiveBehavior::Interrupted) {
+    errno = EINTR;
+    return -1;
+  }
+  if (receive_behavior == ReceiveBehavior::Error) {
+    errno = EIO;
+    return -1;
+  }
+  constexpr std::size_t payload_size = 4;
+  const auto copied = std::min(length, payload_size);
+  std::fill_n(static_cast<std::uint8_t *>(data), copied, 0U);
+  return static_cast<ssize_t>(copied);
 }
 
 TEST(PosixTransportTest, RepeatedEintrPreservesOriginalTimeout) {
-  poll_timeouts.clear();
-  poll_calls = 0;
+  reset_behaviors();
   poll_behavior = PollBehavior::RepeatedEintrThenTimeout;
 
   netft::detail::PosixTransport transport;
@@ -67,8 +127,7 @@ TEST(PosixTransportTest, RepeatedEintrPreservesOriginalTimeout) {
 }
 
 TEST(PosixTransportTest, NonEintrPollErrorStillThrows) {
-  poll_timeouts.clear();
-  poll_calls = 0;
+  reset_behaviors();
   poll_behavior = PollBehavior::Error;
 
   netft::detail::PosixTransport transport;
@@ -80,8 +139,7 @@ TEST(PosixTransportTest, NonEintrPollErrorStillThrows) {
 }
 
 TEST(PosixTransportTest, ExpiredDeadlineDoesNotRepoll) {
-  poll_timeouts.clear();
-  poll_calls = 0;
+  reset_behaviors();
   poll_behavior = PollBehavior::EintrPastDeadline;
 
   netft::detail::PosixTransport transport;
@@ -91,3 +149,87 @@ TEST(PosixTransportTest, ExpiredDeadlineDoesNotRepoll) {
   EXPECT_EQ(transport.receive(buffer.data(), buffer.size(), 20ms), 0U);
   EXPECT_EQ(poll_timeouts.size(), 1U);
 }
+
+TEST(PosixTransportTest, SendBeforeConnectThrows) {
+  reset_behaviors();
+  netft::detail::PosixTransport transport;
+  std::array<std::uint8_t, 8> request{};
+  EXPECT_THROW(transport.send(request), std::runtime_error);
+}
+
+TEST(PosixTransportTest, ReceiveBeforeConnectThrows) {
+  reset_behaviors();
+  netft::detail::PosixTransport transport;
+  std::array<std::uint8_t, 36> buffer{};
+  EXPECT_THROW(transport.receive(buffer.data(), buffer.size(), 20ms), std::runtime_error);
+}
+
+TEST(PosixTransportTest, SendErrorThrows) {
+  reset_behaviors();
+  send_behavior = SendBehavior::Error;
+  netft::detail::PosixTransport transport;
+  transport.connect("127.0.0.1", 49152);
+  std::array<std::uint8_t, 8> request{};
+  EXPECT_THROW(transport.send(request), std::runtime_error);
+}
+
+TEST(PosixTransportTest, ShortSendThrows) {
+  reset_behaviors();
+  send_behavior = SendBehavior::ShortWrite;
+  netft::detail::PosixTransport transport;
+  transport.connect("127.0.0.1", 49152);
+  std::array<std::uint8_t, 8> request{};
+  EXPECT_THROW(transport.send(request), std::runtime_error);
+}
+
+TEST(PosixTransportTest, InvalidPollDescriptorThrows) {
+  reset_behaviors();
+  poll_behavior = PollBehavior::InvalidDescriptor;
+  netft::detail::PosixTransport transport;
+  transport.connect("127.0.0.1", 49152);
+  std::array<std::uint8_t, 36> buffer{};
+  EXPECT_THROW(transport.receive(buffer.data(), buffer.size(), 20ms), std::runtime_error);
+}
+
+TEST(PosixTransportTest, InterruptedReceiveReturnsZero) {
+  reset_behaviors();
+  poll_behavior = PollBehavior::Readable;
+  receive_behavior = ReceiveBehavior::Interrupted;
+  netft::detail::PosixTransport transport;
+  transport.connect("127.0.0.1", 49152);
+  std::array<std::uint8_t, 36> buffer{};
+  EXPECT_EQ(transport.receive(buffer.data(), buffer.size(), 20ms), 0U);
+}
+
+TEST(PosixTransportTest, ReceiveErrorThrows) {
+  reset_behaviors();
+  poll_behavior = PollBehavior::Readable;
+  receive_behavior = ReceiveBehavior::Error;
+  netft::detail::PosixTransport transport;
+  transport.connect("127.0.0.1", 49152);
+  std::array<std::uint8_t, 36> buffer{};
+  EXPECT_THROW(transport.receive(buffer.data(), buffer.size(), 20ms), std::runtime_error);
+}
+
+TEST(PosixTransportTest, ReadableDatagramReturnsPayloadSize) {
+  reset_behaviors();
+  poll_behavior = PollBehavior::Readable;
+  receive_behavior = ReceiveBehavior::Payload;
+  netft::detail::PosixTransport transport;
+  transport.connect("127.0.0.1", 49152);
+  std::array<std::uint8_t, 36> buffer{};
+  EXPECT_EQ(transport.receive(buffer.data(), buffer.size(), 20ms), 4U);
+}
+
+TEST(PosixTransportTest, LargeTimeoutSaturatesPollMilliseconds) {
+  reset_behaviors();
+  poll_behavior = PollBehavior::Timeout;
+  netft::detail::PosixTransport transport;
+  transport.connect("127.0.0.1", 49152);
+  std::array<std::uint8_t, 36> buffer{};
+  const auto timeout = std::chrono::duration<double>{
+      static_cast<double>(std::numeric_limits<int>::max()) / 1000.0 + 1.0};
+  EXPECT_EQ(transport.receive(buffer.data(), buffer.size(), timeout), 0U);
+  ASSERT_EQ(poll_timeouts.size(), 1U);
+  EXPECT_EQ(poll_timeouts.front(), std::numeric_limits<int>::max());
+}