tests: adds require_unless_one test cases

* test: `require_unless_one` with second argument

Add the `require_unless_one_2` test. This tests that when the second
argument in the array is used at the command line, that the required
argument is not present. This test was added because it appears the
`require_unless_one` function only works for the first argument in the
array.

* Fix: assertions for test

The assertions did not check for the `infile` to be present.

tests/require.rs

@@ -279,6 +279,30 @@ fn required_unless_one() {
     assert!(!m.is_present("cfg"));
 }
 
+#[test]
+fn required_unless_one_2() {
+    // This tests that the required_unless_one works when the second arg in the array is used
+    // instead of the first.
+    let res = App::new("unlessone")
+        .arg(Arg::with_name("cfg")
+            .required_unless_one(&["dbg", "infile"])
+            .takes_value(true)
+            .long("config"))
+        .arg(Arg::with_name("dbg")
+            .long("debug"))
+        .arg(Arg::with_name("infile")
+            .short("i")
+            .takes_value(true))
+        .get_matches_from_safe(vec![
+            "unlessone", "-i", "file"
+        ]);
+
+    assert!(res.is_ok());
+    let m = res.unwrap();
+    assert!(m.is_present("infile"));
+    assert!(!m.is_present("cfg"));
+}
+
 #[test]
 fn required_unless_one_err() {
     let res = App::new("unlessone")