feat: More rework

So the performance of this only surpasses list when you approach 100
items (and that is not including the need to traverse through the linked
list to find the insertion point) so this might be the last commit

test/dllist_test.gleam

@@ -1,10 +1,22 @@
 import dllist
+import gleam/dict
 import startest
 
 pub fn main() -> Nil {
   startest.run(startest.default_config())
 }
 
+pub fn new_tests() {
+  startest.describe("new instance", [
+    startest.it("terminated list", fn() {
+      assert dllist.new() == dllist.DLList(1, 0, dict.from_list([]))
+    }),
+    startest.it("cyclic list", fn() {
+      assert dllist.new_cyclic() == dllist.CyclicList(1, 0, dict.from_list([]))
+    }),
+  ])
+}
+
 pub fn is_empty_tests() {
   startest.describe("is_emtpy", [
     startest.it("terminated list", fn() {
@@ -19,3 +31,31 @@ pub fn is_empty_tests() {
     }),
   ])
 }
+
+pub fn from_list_tests() {
+  startest.describe("from_list", [
+    startest.it("terminated list", fn() {
+      assert dllist.is_empty(dllist.from_list([]))
+
+      assert !dllist.is_empty(dllist.from_list([1]))
+
+      assert dllist.from_list([1]) |> dllist.get == Ok(1)
+      assert dllist.from_list([1, 2, 3, 4]) |> dllist.get == Ok(4)
+
+      assert dllist.from_list([1]) |> dllist.to_list == [1]
+      assert dllist.from_list([1, 2, 3, 4]) |> dllist.to_list == [1, 2, 3, 4]
+    }),
+    startest.it("cyclic list", fn() {
+      assert dllist.is_empty(dllist.from_list_cyclic([]))
+
+      assert !dllist.is_empty(dllist.from_list_cyclic([1]))
+
+      assert dllist.from_list_cyclic([1]) |> dllist.get == Ok(1)
+      assert dllist.from_list_cyclic([1, 2, 3, 4]) |> dllist.get == Ok(4)
+
+      assert dllist.from_list_cyclic([1]) |> dllist.to_list == [1]
+      assert dllist.from_list_cyclic([1, 2, 3, 4]) |> dllist.to_list
+        == [4, 1, 2, 3]
+    }),
+  ])
+}