diff --git a/test/source/io.cpp b/test/source/io.cpp
new file mode 100644
index 0000000..e3b5921
--- /dev/null
+++ b/test/source/io.cpp
@@ -0,0 +1,258 @@
+#include <cerrno>
+#include <functional>
+#include <gmock/gmock.h>
+#include <gtest/gtest.h>
+#include <memory>
+#include <sdeventplus/event.hpp>
+#include <sdeventplus/exception.hpp>
+#include <sdeventplus/source/io.hpp>
+#include <sdeventplus/test/sdevent.hpp>
+#include <systemd/sd-event.h>
+#include <type_traits>
+#include <utility>
+
+namespace sdeventplus
+{
+namespace source
+{
+namespace
+{
+
+using testing::DoAll;
+using testing::Return;
+using testing::SaveArg;
+using testing::SetArgPointee;
+
+using UniqueEvent = std::unique_ptr<Event, std::function<void(Event*)>>;
+
+class IOTest : public testing::Test
+{
+  protected:
+    testing::StrictMock<test::SdEventMock> mock;
+    sd_event_source* const expected_source =
+        reinterpret_cast<sd_event_source*>(1234);
+    sd_event* const expected_event = reinterpret_cast<sd_event*>(2345);
+    UniqueEvent event = make_event(expected_event);
+
+    UniqueEvent make_event(sd_event* event)
+    {
+        auto deleter = [this, event](Event* e) {
+            EXPECT_CALL(this->mock, sd_event_unref(event))
+                .WillOnce(Return(nullptr));
+            delete e;
+        };
+        return UniqueEvent(new Event(event, std::false_type(), &mock), deleter);
+    }
+
+    void expect_destruct()
+    {
+        {
+            testing::InSequence sequence;
+            EXPECT_CALL(mock, sd_event_source_set_enabled(expected_source,
+                                                          SD_EVENT_OFF))
+                .WillOnce(Return(0));
+            EXPECT_CALL(mock, sd_event_source_unref(expected_source))
+                .WillOnce(Return(nullptr));
+        }
+        EXPECT_CALL(mock, sd_event_unref(expected_event))
+            .WillOnce(Return(nullptr));
+    }
+};
+
+TEST_F(IOTest, ConstructSuccess)
+{
+    const int fd = 10;
+    const uint32_t events = EPOLLIN | EPOLLET;
+
+    EXPECT_CALL(mock, sd_event_ref(expected_event))
+        .WillOnce(Return(expected_event));
+    sd_event_io_handler_t handler;
+    EXPECT_CALL(mock, sd_event_add_io(expected_event, testing::_, fd, events,
+                                      testing::_, nullptr))
+        .WillOnce(DoAll(SetArgPointee<1>(expected_source), SaveArg<4>(&handler),
+                        Return(0)));
+    void* userdata;
+    EXPECT_CALL(mock, sd_event_source_set_userdata(expected_source, testing::_))
+        .WillOnce(DoAll(SaveArg<1>(&userdata), Return(nullptr)));
+    int completions = 0;
+    int return_fd;
+    uint32_t return_revents;
+    IO::Callback callback = [&](IO&, int fd, uint32_t revents) {
+        return_fd = fd;
+        return_revents = revents;
+        completions++;
+    };
+    IO io(*event, fd, events, std::move(callback));
+    EXPECT_FALSE(callback);
+    EXPECT_EQ(&io, userdata);
+    EXPECT_EQ(0, completions);
+
+    EXPECT_EQ(0, handler(nullptr, 5, EPOLLIN, &io));
+    EXPECT_EQ(1, completions);
+    EXPECT_EQ(5, return_fd);
+    EXPECT_EQ(EPOLLIN, return_revents);
+
+    expect_destruct();
+}
+
+TEST_F(IOTest, ConstructError)
+{
+    const int fd = 10;
+    const uint32_t events = EPOLLIN | EPOLLET;
+
+    EXPECT_CALL(mock, sd_event_add_io(expected_event, testing::_, fd, events,
+                                      testing::_, nullptr))
+        .WillOnce(Return(-EINVAL));
+    int completions = 0;
+    IO::Callback callback = [&completions](IO&, int, uint32_t) {
+        completions++;
+    };
+    EXPECT_THROW(IO(*event, fd, events, std::move(callback)), SdEventError);
+    EXPECT_TRUE(callback);
+    EXPECT_EQ(0, completions);
+}
+
+class IOMethodTest : public IOTest
+{
+  protected:
+    std::unique_ptr<IO> io;
+
+    void SetUp()
+    {
+        const int fd = 7;
+        const int events = EPOLLOUT;
+
+        EXPECT_CALL(mock, sd_event_ref(expected_event))
+            .WillOnce(Return(expected_event));
+        EXPECT_CALL(mock, sd_event_add_io(expected_event, testing::_, fd,
+                                          events, testing::_, nullptr))
+            .WillOnce(DoAll(SetArgPointee<1>(expected_source), Return(0)));
+        EXPECT_CALL(mock,
+                    sd_event_source_set_userdata(expected_source, testing::_))
+            .WillOnce(Return(nullptr));
+        io =
+            std::make_unique<IO>(*event, fd, events, [](IO&, int, uint32_t) {});
+    }
+
+    void TearDown()
+    {
+        expect_destruct();
+        io.reset();
+    }
+};
+
+TEST_F(IOMethodTest, GetFdSuccess)
+{
+    const int fd = 5;
+    EXPECT_CALL(mock, sd_event_source_get_io_fd(expected_source))
+        .WillOnce(Return(fd));
+    EXPECT_EQ(fd, io->get_fd());
+}
+
+TEST_F(IOMethodTest, GetFdError)
+{
+    EXPECT_CALL(mock, sd_event_source_get_io_fd(expected_source))
+        .WillOnce(Return(-EINVAL));
+    EXPECT_THROW(io->get_fd(), SdEventError);
+}
+
+TEST_F(IOMethodTest, SetFdSuccess)
+{
+    const int fd = 5;
+    EXPECT_CALL(mock, sd_event_source_set_io_fd(expected_source, fd))
+        .WillOnce(Return(0));
+    io->set_fd(fd);
+}
+
+TEST_F(IOMethodTest, SetFdError)
+{
+    const int fd = 3;
+    EXPECT_CALL(mock, sd_event_source_set_io_fd(expected_source, fd))
+        .WillOnce(Return(-EINVAL));
+    EXPECT_THROW(io->set_fd(fd), SdEventError);
+}
+
+TEST_F(IOMethodTest, GetFdOwnSuccess)
+{
+    EXPECT_CALL(mock, sd_event_source_get_io_fd_own(expected_source))
+        .WillOnce(Return(3));
+    EXPECT_TRUE(io->get_fd_own());
+    EXPECT_CALL(mock, sd_event_source_get_io_fd_own(expected_source))
+        .WillOnce(Return(0));
+    EXPECT_FALSE(io->get_fd_own());
+}
+
+TEST_F(IOMethodTest, GetFdOwnError)
+{
+    EXPECT_CALL(mock, sd_event_source_get_io_fd_own(expected_source))
+        .WillOnce(Return(-EINVAL));
+    EXPECT_THROW(io->get_fd_own(), SdEventError);
+}
+
+TEST_F(IOMethodTest, SetFdOwnSuccess)
+{
+    EXPECT_CALL(mock, sd_event_source_set_io_fd_own(expected_source, true))
+        .WillOnce(Return(0));
+    io->set_fd_own(true);
+}
+
+TEST_F(IOMethodTest, SetFdOwnError)
+{
+    EXPECT_CALL(mock, sd_event_source_set_io_fd_own(expected_source, false))
+        .WillOnce(Return(-EINVAL));
+    EXPECT_THROW(io->set_fd_own(false), SdEventError);
+}
+
+TEST_F(IOMethodTest, GetEventsSuccess)
+{
+    const uint32_t events = EPOLLIN | EPOLLOUT;
+    EXPECT_CALL(mock,
+                sd_event_source_get_io_events(expected_source, testing::_))
+        .WillOnce(DoAll(SetArgPointee<1>(events), Return(0)));
+    EXPECT_EQ(events, io->get_events());
+}
+
+TEST_F(IOMethodTest, GetEventsError)
+{
+    EXPECT_CALL(mock,
+                sd_event_source_get_io_events(expected_source, testing::_))
+        .WillOnce(Return(-EINVAL));
+    EXPECT_THROW(io->get_events(), SdEventError);
+}
+
+TEST_F(IOMethodTest, SetEventsSuccess)
+{
+    const uint32_t events = EPOLLIN | EPOLLOUT;
+    EXPECT_CALL(mock, sd_event_source_set_io_events(expected_source, events))
+        .WillOnce(Return(0));
+    io->set_events(events);
+}
+
+TEST_F(IOMethodTest, SetEventsError)
+{
+    const uint32_t events = EPOLLIN | EPOLLOUT;
+    EXPECT_CALL(mock, sd_event_source_set_io_events(expected_source, events))
+        .WillOnce(Return(-EINVAL));
+    EXPECT_THROW(io->set_events(events), SdEventError);
+}
+
+TEST_F(IOMethodTest, GetREventsSuccess)
+{
+    const uint32_t revents = EPOLLOUT;
+    EXPECT_CALL(mock,
+                sd_event_source_get_io_revents(expected_source, testing::_))
+        .WillOnce(DoAll(SetArgPointee<1>(revents), Return(0)));
+    EXPECT_EQ(revents, io->get_revents());
+}
+
+TEST_F(IOMethodTest, GetREventsError)
+{
+    EXPECT_CALL(mock,
+                sd_event_source_get_io_revents(expected_source, testing::_))
+        .WillOnce(Return(-EINVAL));
+    EXPECT_THROW(io->get_revents(), SdEventError);
+}
+
+} // namespace
+} // namespace source
+} // namespace sdeventplus