Add new test for grade-school exersice (#1204)

* Add new test to GradeSchoolTests

* Revert "Add new test to GradeSchoolTests"

This reverts commit e6d6aad.

* Add new test to GradeSchoolTests. No formatting

exercises/practice/grade-school/GradeSchoolTests.fs

@@ -139,3 +139,15 @@ let ``Students are sorted by name in a grade`` () =
         |> add "Jeff" 1
     grade 5 school |> should equal ["Bradley"; "Franklin"]
 
+[<Fact(Skip = "Remove this Skip property to run this test")>]
+let ``Students are sorted by grades and then by name in the roster even when school was not sorted``() =
+    let school =
+        seq {
+            1, [ "Anna"; "Charlie"; "Barb" ]
+            2, [ "Peter"; "Zoe"; "Alex" ]
+            3, [ "Jim" ]
+        }
+        |> Map.ofSeq
+    roster school
+    |> should equal [ "Anna"; "Barb"; "Charlie"; "Alex"; "Peter"; "Zoe"; "Jim" ]
+