diff --git a/lab04/data1.txt b/lab04/data1.txt
new file mode 100644
index 0000000..f9f3ad0
--- /dev/null
+++ b/lab04/data1.txt
@@ -0,0 +1,5 @@
+homer simpson 25 # bad at nuclear engineering
+ ned flanders 12 !! valid
+    waylon   smithers  100 ! high score
+  gary chalmers 5
+monty burns
diff --git a/lab04/data2.txt b/lab04/data2.txt
new file mode 100644
index 0000000..3bef19d
--- /dev/null
+++ b/lab04/data2.txt
@@ -0,0 +1 @@
+monty burns
diff --git a/lab04/records.ml b/lab04/records.ml
index 6c02ff7..8744d71 100644
--- a/lab04/records.ml
+++ b/lab04/records.ml
@@ -1,7 +1,19 @@
+(** [record] of a person with a first name, last name, and score *)
 type record = {firstname: string; lastname: string; score: int};;
 
+(** [new_records f l s] creates a new record with the given firstname [f],
+  * lastname [l] and score [s] *)
 let new_record f l s = {firstname = f; lastname = l; score = s};;
 
+(**/**)
+let test_new_record () =
+  assert (new_record "a" "b" 1 = {firstname = "a"; lastname = "b"; score = 1});
+  assert (new_record "b" "a" 2 = {firstname = "b"; lastname = "a"; score = 2});
+  assert (new_record "c" "d" 3 = {firstname = "c"; lastname = "d"; score = 3})
+(**/**)
+
+(** [print_records r] takes a list of records [r] and prints
+  * each record neatly to the console *)
 let rec print_records r =
   match r with
   | [] -> ()
@@ -15,12 +27,59 @@ let rec records_insert x l =
   | y :: ys when x.score < y.score -> y :: records_insert x ys
   | _ -> x :: l
 
+(**/**)
+let test_records_insert () =
+  assert (records_insert
+    {firstname = "a"; lastname = "b"; score = 1} [] =
+    [{firstname = "a"; lastname = "b"; score = 1}]
+  );
+  assert (records_insert
+    {firstname = "a"; lastname = "b"; score = 1}
+    [{firstname = "c"; lastname = "d"; score = 2}] =
+  [
+    {firstname = "c"; lastname = "d"; score = 2};
+    {firstname = "a"; lastname = "b"; score = 1}
+  ]);
+  assert (records_insert
+    {firstname = "e"; lastname = "f"; score = 2}
+    [
+      {firstname = "c"; lastname = "d"; score = 3};
+      {firstname = "a"; lastname = "b"; score = 1}
+    ] =
+    [
+      {firstname = "c"; lastname = "d"; score = 3};
+      {firstname = "e"; lastname = "f"; score = 2};
+      {firstname = "a"; lastname = "b"; score = 1}
+    ])
+(**/**)
+
 (** [records_insertion_sort l] sorts list of records [l] in ascending order *)
-let rec records_insertion_sort l =
+let rec sort_records l =
   match l with
   | [] -> []
-  | x :: xs -> records_insert x (records_insertion_sort xs)
+  | x :: xs -> records_insert x (sort_records xs)
 
+(**/**)
+let test_sort_records () =
+  assert (sort_records [] = []);
+  assert (sort_records
+    [{firstname = "a"; lastname = "b"; score = 1}] =
+    [{firstname = "a"; lastname = "b"; score = 1}]);
+
+  assert (sort_records [
+    {firstname = "c"; lastname = "d"; score = 3};
+    {firstname = "a"; lastname = "b"; score = 1};
+    {firstname = "e"; lastname = "f"; score = 2};
+  ] = [
+    {firstname = "c"; lastname = "d"; score = 3};
+    {firstname = "e"; lastname = "f"; score = 2};
+    {firstname = "a"; lastname = "b"; score = 1};
+  ])
+(**/**)
+
+(** [parse l] takes in a line [l] and parses the line to extract
+  * firstname, lastname, and score, returning Some record if successful
+  * or None if the input line [l] contains bad data *)
 let rec parse l =
   try
     Scanf.sscanf l " %s %s %s" (fun f l s ->
@@ -31,6 +90,21 @@ let rec parse l =
   with
   | Scanf.Scan_failure _ -> None
 
+(**/**)
+let test_parse () =
+  assert (parse "" = None);
+  assert (parse "Bart simpson 5abc" = None);
+  assert (parse "Lisa simpson 130" = None);
+  assert (parse "Homer Simpson -5" = None);
+  assert (parse "Homer Simpson 5" =
+    Some {firstname = "Homer"; lastname = "Simpson"; score = 5});
+  assert (parse "Homer Simpson 5 blah blah blah" =
+    Some {firstname = "Homer"; lastname = "Simpson"; score = 5})
+(**/**)
+
+(** [read_file acc ic] takes in an accumulator [acc] and an input channel [ic]
+  * and oterates over it input channel [ic] to parse each line and store the
+  * parsed result into the accumulator [acc] *)
 let rec read_file acc ic =
   try
     match parse @@ input_line ic with
@@ -39,9 +113,35 @@ let rec read_file acc ic =
   with
   | End_of_file -> close_in ic; acc
 
+(**/**)
+let test_read_file () =
+  assert (read_file [] @@ open_in "data.txt" = [
+    {firstname = "gary"; lastname = "chalmers"; score = 5};
+    {firstname = "waylon"; lastname = "smithers"; score = 100};
+    {firstname = "homer"; lastname = "simpson"; score = 25};
+  ]);
+  assert (read_file [] @@ open_in "data1.txt" = [
+    {firstname = "gary"; lastname = "chalmers"; score = 5};
+    {firstname = "waylon"; lastname = "smithers"; score = 100};
+    {firstname = "ned"; lastname = "flanders"; score = 12};
+    {firstname = "homer"; lastname = "simpson"; score = 25};
+  ]);
+  assert (read_file [] @@ open_in "data2.txt" = [])
+(**/**)
+
+(**/**)
+let run_all_tests () =
+  test_new_record();
+  test_parse();
+  test_read_file();
+  test_records_insert();
+  test_sort_records()
+(**/**)
+
+(** main program entry from cli *)
 let () =
   if Array.length Sys.argv = 1 then
     Printf.printf "%s: expects 1 file input.\nUsage: \"%s <filename>\"\n" Sys.argv.(0) Sys.argv.(0)
   else
     let ic = open_in Sys.argv.(1) in
-    print_records @@ records_insertion_sort @@ read_file [] ic;;
+    print_records @@ sort_records @@ read_file [] ic;;