tests/sort: add tests for month sort

tests/fixtures/sort/month1.ans

@@ -0,0 +1,7 @@
+N/A Ut enim ad minim veniam, quis
+Jan Lorem ipsum dolor sit amet
+mar laboris nisi ut aliquip ex ea
+May sed do eiusmod tempor incididunt
+JUN nostrud exercitation ullamco
+Oct ut labore et dolore magna aliqua
+Dec consectetur adipiscing elit

tests/fixtures/sort/month1.txt

@@ -0,0 +1,7 @@
+Jan Lorem ipsum dolor sit amet
+Dec consectetur adipiscing elit
+May sed do eiusmod tempor incididunt
+Oct ut labore et dolore magna aliqua
+N/A Ut enim ad minim veniam, quis
+JUN nostrud exercitation ullamco
+mar laboris nisi ut aliquip ex ea

tests/sort.rs

@@ -41,6 +41,11 @@ fn human1() {
     test_helper(&String::from("human1"), &String::from("-H"));
 }
 
+#[test]
+fn month1() {
+    test_helper(&String::from("month1"), &String::from("-M"));
+}
+
 fn numeric_helper(test_num: isize) {
     test_helper(&format!("numeric{}", test_num), &String::from("-n"))
 }