diff --git a/CMakeLists.txt b/CMakeLists.txt
index 2508a1bb..03ff80e3 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -11,6 +11,9 @@ target_include_directories(Catch INTERFACE ${CATCH_INCLUDE_DIR})
 set(TEST_SOURCES 
 	Tests/tests.cpp
 	Tests/Example_test.cpp
+	Tests/Timer_test.cpp
+	Firmware/Timer.cpp
 )
 add_executable(tests ${TEST_SOURCES})
+target_include_directories(tests PRIVATE Tests)
 target_link_libraries(tests Catch)
diff --git a/Tests/Arduino.h b/Tests/Arduino.h
new file mode 100644
index 00000000..c6740d5e
--- /dev/null
+++ b/Tests/Arduino.h
@@ -0,0 +1,12 @@
+/**
+ * @file
+ * @brief Mock file to allow test compilation.
+ * @author  Marek Bel
+ */
+
+#ifndef TESTS_ARDUINO_H_
+#define TESTS_ARDUINO_H_
+
+extern unsigned long millis();
+
+#endif /* TESTS_ARDUINO_H_ */
diff --git a/Tests/Timer_test.cpp b/Tests/Timer_test.cpp
new file mode 100644
index 00000000..9bcf1f99
--- /dev/null
+++ b/Tests/Timer_test.cpp
@@ -0,0 +1,34 @@
+/**
+ * @file
+ * @author Marek Bel
+ */
+
+
+#include "catch.hpp"
+#include "../Firmware/Timer.h"
+
+unsigned long millis()
+{
+    return 1;
+}
+
+TEST_CASE( "LongTimer tested.", "[timer]" )
+{
+    LongTimer timer;
+    REQUIRE( timer.running() == false);
+
+    timer.start();
+    REQUIRE( timer.running() == true);
+
+    timer.stop();
+    REQUIRE( timer.running() == false);
+
+    timer.start();
+    REQUIRE( timer.expired(0) == true );
+    REQUIRE( timer.expired(0) == false );
+    REQUIRE( timer.running() == false);
+
+    timer.start();
+    REQUIRE( timer.expired(1) == false );
+    REQUIRE( timer.running() == true);
+}