Implemented input handler test for valid method

test/test_inputHandler.c

@@ -23,3 +23,10 @@ void test_inputHandler_returnoneforinputplus(void) {
     result = getOperationIdBySymbol('+');
     TEST_ASSERT_EQUAL_INT(expectedResult, result);
 }
+
+void test_inputHandler_returnzeroforinvalidinput(void) {
+    int expectedResult = 0;
+    int result;
+    result = isOperationIdValid(0);
+    TEST_ASSERT_EQUAL_INT(expectedResult, result);
+}