Implement Sub find test

test/test_inputHandling.c

@@ -47,4 +47,11 @@ void test_inputHandling_findAddFunctionType(void)
     TEST_ASSERT_TRUE(opAdd == type);
 }
 
+void test_inputHandling_findSubFunctionType(void)
+{
+    op type = opNotSupported;
+    type = detectFunctionOperator("4-5", 3);
+    TEST_ASSERT_TRUE(opSub == type);
+}
+
 #endif // TEST