Add test case for missing expected positional argument

This fills a tiny gap in the positional_arguments suite.  Most existing
tests have positional arguments.  The one case without an argument uses
Argument::remaining so that ArgumentParserArgument::parse_args does not
throw, instead ArgumentParser::get<> throws std::logic_error.

Signed-off-by: Sean Robinson <sean.robinson@scottsdalecc.edu>

test/test_positional_arguments.cpp

@@ -13,6 +13,15 @@ TEST_CASE("Parse positional arguments" * test_suite("positional_arguments")) {
   REQUIRE(program.get("output") == "thrust_profile.csv");
 }
 
+TEST_CASE("Missing expected positional argument" *
+          test_suite("positional_arguments")) {
+  argparse::ArgumentParser program("test");
+  program.add_argument("input");
+  REQUIRE_THROWS_WITH_AS(program.parse_args({ "test" }),
+                         "1 argument(s) expected. 0 provided.",
+                         std::runtime_error);
+}
+
 TEST_CASE("Parse positional arguments with fixed nargs" *
           test_suite("positional_arguments")) {
   argparse::ArgumentParser program("test");