source/child: Implement
diff --git a/test/source/child.cpp b/test/source/child.cpp
new file mode 100644
index 0000000..e1e1322
--- /dev/null
+++ b/test/source/child.cpp
@@ -0,0 +1,163 @@
+#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/child.hpp>
+#include <sdeventplus/test/sdevent.hpp>
+#include <sys/wait.h>
+#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 ChildTest : 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(ChildTest, ConstructSuccess)
+{
+    const pid_t pid = 50;
+    const int options = WEXITED;
+
+    EXPECT_CALL(mock, sd_event_ref(expected_event))
+        .WillOnce(Return(expected_event));
+    sd_event_child_handler_t handler;
+    EXPECT_CALL(mock, sd_event_add_child(expected_event, testing::_, pid,
+                                         options, 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;
+    const siginfo_t* return_si;
+    Child::Callback callback = [&](Child&, const siginfo_t* si) {
+        return_si = si;
+        completions++;
+    };
+    Child child(*event, pid, options, std::move(callback));
+    EXPECT_FALSE(callback);
+    EXPECT_EQ(&child, userdata);
+    EXPECT_EQ(0, completions);
+
+    const siginfo_t* expected_si = reinterpret_cast<siginfo_t*>(865);
+    EXPECT_EQ(0, handler(nullptr, expected_si, &child));
+    EXPECT_EQ(1, completions);
+    EXPECT_EQ(expected_si, return_si);
+
+    expect_destruct();
+}
+
+TEST_F(ChildTest, ConstructError)
+{
+    const pid_t pid = 50;
+    const int options = WEXITED;
+
+    EXPECT_CALL(mock, sd_event_add_child(expected_event, testing::_, pid,
+                                         options, testing::_, nullptr))
+        .WillOnce(Return(-EINVAL));
+    int completions = 0;
+    Child::Callback callback = [&completions](Child&, const siginfo_t*) {
+        completions++;
+    };
+    EXPECT_THROW(Child(*event, pid, options, std::move(callback)),
+                 SdEventError);
+    EXPECT_TRUE(callback);
+    EXPECT_EQ(0, completions);
+}
+
+class ChildMethodTest : public ChildTest
+{
+  protected:
+    std::unique_ptr<Child> child;
+
+    void SetUp()
+    {
+        const pid_t pid = 50;
+        const int options = WEXITED;
+
+        EXPECT_CALL(mock, sd_event_ref(expected_event))
+            .WillOnce(Return(expected_event));
+        EXPECT_CALL(mock, sd_event_add_child(expected_event, testing::_, pid,
+                                             options, testing::_, nullptr))
+            .WillOnce(DoAll(SetArgPointee<1>(expected_source), Return(0)));
+        EXPECT_CALL(mock,
+                    sd_event_source_set_userdata(expected_source, testing::_))
+            .WillOnce(Return(nullptr));
+        child = std::make_unique<Child>(*event, pid, options,
+                                        [](Child&, const siginfo_t*) {});
+    }
+
+    void TearDown()
+    {
+        expect_destruct();
+        child.reset();
+    }
+};
+
+TEST_F(ChildMethodTest, GetPidSuccess)
+{
+    const pid_t pid = 32;
+    EXPECT_CALL(mock,
+                sd_event_source_get_child_pid(expected_source, testing::_))
+        .WillOnce(DoAll(SetArgPointee<1>(pid), Return(0)));
+    EXPECT_EQ(pid, child->get_pid());
+}
+
+TEST_F(ChildMethodTest, GetPidError)
+{
+    EXPECT_CALL(mock,
+                sd_event_source_get_child_pid(expected_source, testing::_))
+        .WillOnce(Return(-EINVAL));
+    EXPECT_THROW(child->get_pid(), SdEventError);
+}
+
+} // namespace
+} // namespace source
+} // namespace sdeventplus