Address PR feedback: add tests

info.toml

@@ -617,17 +617,17 @@ hint = """
 [[exercises]]
 name = "box1"
 path = "exercises/standard_library_types/box1.rs"
-mode = "compile"
+mode = "test"
 hint = """
 Step 1
 The compiler's message should help: since we cannot store the value of the actual type
 when working with recursive types, we need to store a reference (pointer) to its value.
-We should therefore place our `List` inside a `Box`. More details in the book here:
+We should, therefore, place our `List` inside a `Box`. More details in the book here:
 https://doc.rust-lang.org/book/ch15-01-box.html#enabling-recursive-types-with-boxes
 
 Step 2
 Creating an empty list should be fairly straightforward (hint: peek at the assertions).
-For a non-empty list keep in mind that wee want to use our Cons "list builder".
+For a non-empty list keep in mind that we want to use our Cons "list builder".
 Although the current list is one of integers (i32), feel free to change the definition
 and try other types!
 """