diff --git a/test/source/child.cpp b/test/source/child.cpp
index e1e1322..ab173b1 100644
--- a/test/source/child.cpp
+++ b/test/source/child.cpp
@@ -91,6 +91,10 @@
     EXPECT_EQ(1, completions);
     EXPECT_EQ(expected_si, return_si);
 
+    child.set_callback(std::bind([]() {}));
+    EXPECT_EQ(0, handler(nullptr, expected_si, &child));
+    EXPECT_EQ(1, completions);
+
     expect_destruct();
 }
 
diff --git a/test/source/event.cpp b/test/source/event.cpp
index 90edaec..e4d7b2a 100644
--- a/test/source/event.cpp
+++ b/test/source/event.cpp
@@ -83,6 +83,10 @@
     EXPECT_EQ(0, handler(nullptr, &defer));
     EXPECT_EQ(1, completions);
 
+    defer.set_callback(std::bind([]() {}));
+    EXPECT_EQ(0, handler(nullptr, &defer));
+    EXPECT_EQ(1, completions);
+
     expect_destruct();
 }
 
diff --git a/test/source/io.cpp b/test/source/io.cpp
index b680be7..89506b1 100644
--- a/test/source/io.cpp
+++ b/test/source/io.cpp
@@ -92,6 +92,10 @@
     EXPECT_EQ(5, return_fd);
     EXPECT_EQ(EPOLLIN, return_revents);
 
+    io.set_callback(std::bind([]() {}));
+    EXPECT_EQ(0, handler(nullptr, 5, EPOLLIN, &io));
+    EXPECT_EQ(1, completions);
+
     expect_destruct();
 }
 
diff --git a/test/source/signal.cpp b/test/source/signal.cpp
index c99aa6b..d3b53a7 100644
--- a/test/source/signal.cpp
+++ b/test/source/signal.cpp
@@ -92,6 +92,10 @@
     EXPECT_EQ(1, completions);
     EXPECT_EQ(expected_si, return_si);
 
+    signal.set_callback(std::bind([]() {}));
+    EXPECT_EQ(0, handler(nullptr, expected_si, &signal));
+    EXPECT_EQ(1, completions);
+
     expect_destruct();
 }
 
diff --git a/test/source/time.cpp b/test/source/time.cpp
index aa25da0..96a920e 100644
--- a/test/source/time.cpp
+++ b/test/source/time.cpp
@@ -90,6 +90,11 @@
     EXPECT_EQ(Time<id>::TimePoint(std::chrono::microseconds(2000100)),
               saved_time);
 
+    time.set_callback(std::bind([]() {}));
+    EXPECT_EQ(0, handler(nullptr, 0, userdata));
+    EXPECT_EQ(Time<id>::TimePoint(std::chrono::microseconds(2000100)),
+              saved_time);
+
     expect_time_destroy(expected_event, expected_source);
 }