input test

test/test.cpp

@@ -65,3 +65,13 @@ TEST_CASE( "Unrecognized characters are detected and exception is thrown", "[cal
   REQUIRE_THROWS_AS( evaluate("11+3?4"), std::invalid_argument );
   REQUIRE_THROWS_AS( evaluate("1F+"), std::invalid_argument );
 }
+
+TEST_CASE("Exceptions is thrown if input contains only operands", "[calc]") {
+  REQUIRE_THROWS(evaluate("+"));
+  REQUIRE_THROWS(evaluate("-"));
+  REQUIRE_THROWS(evaluate("*"));
+  REQUIRE_THROWS(evaluate("/"));
+  REQUIRE_THROWS(evaluate("+++"));
+  REQUIRE_THROWS(evaluate("+----"));
+  REQUIRE_THROWS(evaluate("*-*-///"));  
+}